/* ==========================================================================
   Scale Model — tokens, shell and shared widgets.

   The look is an engineer's schematic: hairlines, 2px corners, mono numbers,
   a faint drafting grid, corner ticks on the parts that matter. The request
   shapes (see .sm-state) are the only bright things on screen.

   Literal colours appear ONLY in the three token blocks below. Everything else,
   including css/sim.css and css/m1…m5.css, uses the tokens.

   Contents
     1 Tokens            5 Home              9 Motion and print
     2 Base              6 Lesson page
     3 Helpers           7 Cheat sheet
     4 Shell             8 Widgets (.sm-*)
   ========================================================================== */

/* ---- 1. Tokens ---------------------------------------------------------- */

:root {
  color-scheme: light;

  --bg: #F3F5F2;
  --surface: #FFFFFF;
  --surface-2: #E7EBE6;
  --line: #CDD4CE;
  --ink: #151D19;
  --ink-2: #566259;
  --accent: #0B6E55;
  --on-accent: #FFFFFF;

  /* request and part states: always paired with a shape or a label */
  --ok: #1E8A4C;       /* round dot */
  --slow: #B26A00;     /* diamond */
  --fail: #C8322B;     /* cross */
  --cached: #2F6FED;   /* ring */

  /* chart series that are not states (dash pattern + label carry identity too) */
  --series-c: #7A4FD0;
  --series-d: #B4541A;

  --shadow-float: 0 10px 28px rgb(21 29 25 / 0.16), 0 2px 6px rgb(21 29 25 / 0.08);
  --scrim: rgb(21 29 25 / 0.42);

  /* derived: token-only, so they follow the theme without being repeated */
  --good: var(--ok);
  --warn: var(--slow);
  --bad: var(--fail);
  --series-a: var(--ink);
  --series-b: var(--accent);
  --line-strong: color-mix(in oklab, var(--line) 35%, var(--ink-2));   /* 3:1 on surface and bg: control borders */
  --accent-soft: color-mix(in oklab, var(--accent) 10%, var(--surface));
  --accent-hover: color-mix(in oklab, var(--accent) 86%, var(--ink));
  --ok-soft: color-mix(in oklab, var(--ok) 12%, var(--surface));
  --slow-soft: color-mix(in oklab, var(--slow) 12%, var(--surface));
  --fail-soft: color-mix(in oklab, var(--fail) 12%, var(--surface));
  --cached-soft: color-mix(in oklab, var(--cached) 12%, var(--surface));
  --grid: color-mix(in oklab, var(--line) 38%, transparent);

  /* type */
  --font-display: "Archivo", "Arial Nova", "Helvetica Neue", "Segoe UI", Arial, sans-serif;
  --font-body: "IBM Plex Sans", "Segoe UI", system-ui, -apple-system, Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-mono: "IBM Plex Mono", ui-monospace, "SF Mono", "Cascadia Mono", Menlo, Consolas, "Liberation Mono", monospace;

  --fs-micro: 0.6875rem;  /* 11 */
  --fs-xs: 0.75rem;       /* 12 */
  --fs-sm: 0.8125rem;     /* 13 */
  --fs-base: 1rem;        /* 16 */
  --fs-md: 1.125rem;      /* 18 */
  --fs-lg: 1.375rem;      /* 22 */
  --fs-xl: clamp(1.75rem, 1.3rem + 1.9vw, 2.5rem);          /* 28–40 */
  --fs-idea: clamp(1.25rem, 1.05rem + 0.9vw, 1.625rem);     /* 20–26 */

  /* space */
  --s1: 4px;
  --s2: 8px;
  --s3: 12px;
  --s4: 16px;
  --s5: 24px;
  --s6: 32px;
  --s7: 48px;
  --s8: 72px;

  --radius: 2px;
  --rail-w: 268px;
  --bar-h: 52px;
  --content-w: 1080px;
  --measure: 60ch;
  --tick: 9px;            /* length of a corner tick */
  --cell: 24px;           /* drafting grid */
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    color-scheme: dark;
    --bg: #0F1412;
    --surface: #171D1A;
    --surface-2: #202825;
    --line: #2D3733;
    --ink: #E9EEEA;
    --ink-2: #98A69D;
    --accent: #4FD1A5;
    --on-accent: #06231A;
    --ok: #4CC38A;
    --slow: #F1A10D;
    --fail: #FF6369;
    --cached: #7AA7FF;
    --series-c: #9477EE;
    --series-d: #CC7646;
    --shadow-float: 0 12px 32px rgb(0 0 0 / 0.55), 0 2px 6px rgb(0 0 0 / 0.4);
    --scrim: rgb(0 0 0 / 0.6);
  }
}

:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #0F1412;
  --surface: #171D1A;
  --surface-2: #202825;
  --line: #2D3733;
  --ink: #E9EEEA;
  --ink-2: #98A69D;
  --accent: #4FD1A5;
  --on-accent: #06231A;
  --ok: #4CC38A;
  --slow: #F1A10D;
  --fail: #FF6369;
  --cached: #7AA7FF;
  --series-c: #9477EE;
  --series-d: #CC7646;
  --shadow-float: 0 12px 32px rgb(0 0 0 / 0.55), 0 2px 6px rgb(0 0 0 / 0.4);
  --scrim: rgb(0 0 0 / 0.6);
}

/* ---- 2. Base ------------------------------------------------------------ */

*, *::before, *::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-padding-top: calc(var(--bar-h) + var(--s4));
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: var(--fs-base);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  overflow-wrap: break-word;
  /* the drafting grid: faint enough to sit under text */
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: var(--cell) var(--cell);
  background-position: -1px -1px;
}

[hidden] { display: none !important; }

h1, h2, h3, h4, p, ul, ol, figure, blockquote { margin: 0; }
ul, ol { padding: 0; list-style: none; }
h1, h2, h3 { text-wrap: balance; line-height: 1.15; }
p { text-wrap: pretty; max-width: var(--measure); }
img, svg, canvas { display: block; max-width: 100%; }
button, input, select, textarea { font: inherit; color: inherit; }
button { cursor: pointer; border-radius: var(--radius); }
a { color: var(--accent); text-underline-offset: 0.18em; text-decoration-thickness: 1px; }
a:hover { text-decoration-thickness: 2px; }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: var(--radius);
}
[tabindex="-1"]:focus { outline: none; }

::selection { background: color-mix(in oklab, var(--accent) 28%, transparent); }

.icon { width: 1em; height: 1em; flex: none; }

.visually-hidden {
  position: absolute !important;
  width: 1px; height: 1px;
  margin: -1px; padding: 0; border: 0;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

/* ---- 3. Helpers for lesson authors -------------------------------------- */

.mono {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  letter-spacing: -0.01em;
}

/* drawing annotation: small mono capitals, the lettering of a title block */
.micro {
  font-family: var(--font-mono);
  font-size: var(--fs-micro);
  font-weight: 500;
  line-height: 1.3;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--ink-2);
}

.caption {
  font-size: var(--fs-sm);
  line-height: 1.45;
  color: var(--ink-2);
  max-width: var(--measure);
}

.note {
  padding-left: var(--s3);
  border-left: 2px solid var(--line-strong);
  font-size: 0.9375rem;
  line-height: 1.45;
  max-width: var(--measure);
}

.big-number {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: clamp(1.75rem, 1.4rem + 1.4vw, 2.5rem);
  font-weight: 500;
  line-height: 1;
  letter-spacing: -0.04em;
  color: var(--ink);
}

.stack { display: flex; flex-direction: column; gap: var(--s4); min-width: 0; }
.stack--sm { gap: var(--s2); }
.stack--lg { gap: var(--s6); }

.row { display: flex; flex-wrap: wrap; align-items: center; gap: var(--s3); min-width: 0; }
.row--top { align-items: flex-start; }
.row--end { align-items: flex-end; }
.row--between { justify-content: space-between; }
.row > .grow, .grow { flex: 1 1 0; min-width: 0; }

.grid-2, .grid-3 { display: grid; gap: var(--s5); min-width: 0; }
.grid-2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid-3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.grid-2 > *, .grid-3 > * { min-width: 0; }
@media (max-width: 720px) {
  .grid-2, .grid-3 { grid-template-columns: minmax(0, 1fr); }
}
@media (min-width: 721px) and (max-width: 1100px) {
  .grid-3 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

/* a strip of controls beside or under the simulator: as many columns as fit */
.controls {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 210px), 1fr));
  gap: var(--s4) var(--s5);
  align-items: end;
  min-width: 0;
}
.controls > * { min-width: 0; }

.panel {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: var(--s4);
  min-width: 0;
}
.panel--flush { padding: 0; overflow: hidden; }
.panel--sunken { background: var(--surface-2); border-color: transparent; }

/* corner ticks, like the registration marks on a drawing sheet */
.ticks, .panel--ticks { position: relative; }
.ticks::before, .panel--ticks::before {
  content: "";
  position: absolute;
  inset: -1px;
  pointer-events: none;
  --c: linear-gradient(var(--ink), var(--ink));
  background:
    var(--c) left top / var(--tick) 1px no-repeat, var(--c) left top / 1px var(--tick) no-repeat,
    var(--c) right top / var(--tick) 1px no-repeat, var(--c) right top / 1px var(--tick) no-repeat,
    var(--c) left bottom / var(--tick) 1px no-repeat, var(--c) left bottom / 1px var(--tick) no-repeat,
    var(--c) right bottom / var(--tick) 1px no-repeat, var(--c) right bottom / 1px var(--tick) no-repeat;
}

/* inline-sized widgets keep their own width inside vertical stacks */
:is(.stack, .lesson-section__body, .sm-challenge__body, .lesson-body) > :is(.btn, .sm-seg-wrap, .sm-toggle, .sm-stepper, .sm-state, .sm-legend, .kind-tag) {
  align-self: flex-start;
}

/* wide content scrolls inside its own box, never the page */
.scroll-x { overflow-x: auto; max-width: 100%; overscroll-behavior-x: contain; }

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--s2);
  min-height: 36px;
  padding: 6px 14px;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--ink);
  font-size: 0.875rem;
  font-weight: 600;
  line-height: 1.2;
  text-decoration: none;
  transition: background-color 0.12s, border-color 0.12s;
}
.btn:hover { background: var(--surface-2); border-color: var(--ink-2); }
.btn[disabled], .btn[aria-disabled="true"] { opacity: 0.5; cursor: not-allowed; }
.btn--primary { background: var(--accent); border-color: var(--accent); color: var(--on-accent); }
.btn--primary:hover { background: var(--accent-hover); border-color: var(--accent-hover); }
.btn--quiet { border-color: transparent; background: transparent; color: var(--ink-2); }
.btn--quiet:hover { color: var(--ink); background: var(--surface-2); border-color: transparent; }
.btn--sm { min-height: 30px; padding: 3px 10px; font-size: var(--fs-sm); }
.btn .icon { font-size: 1rem; }

/* segmented meter: progress drawn as cells, not a rounded bar */
.sm-meter { display: flex; gap: 6px; min-width: 0; }
.sm-meter__group { display: flex; gap: 2px; min-width: 0; }
.sm-meter__seg {
  flex: 1 1 0;
  min-width: 2px;
  height: 8px;
  border: 1px solid var(--line-strong);
  border-radius: 1px;
  background: transparent;
}
.sm-meter__seg.is-on { background: var(--accent); border-color: var(--accent); }
.sm-meter--lg .sm-meter__seg { height: 14px; }

/* a state shape with its label: never colour alone */
.sm-state { display: inline-flex; align-items: center; gap: 6px; font-size: var(--fs-sm); line-height: 1.2; color: var(--ink); white-space: nowrap; }
.sm-state .icon { font-size: 0.75rem; }
.sm-state--ok .icon { color: var(--ok); }
.sm-state--slow .icon { color: var(--slow); }
.sm-state--fail .icon { color: var(--fail); }
.sm-state--cached .icon { color: var(--cached); }

/* touch: every control is at least 40px tall */
@media (max-width: 859.98px), (pointer: coarse) {
  .btn, .btn--sm { min-height: 40px; }
}

/* ---- 4. Shell ----------------------------------------------------------- */

.app {
  display: grid;
  grid-template-columns: var(--rail-w) minmax(0, 1fr);
  min-height: 100vh;
  min-height: 100dvh;
}

.skip-link {
  position: fixed;
  left: var(--s3); top: var(--s3);
  z-index: 100;
  padding: 8px 12px;
  background: var(--surface);
  border: 1px solid var(--line-strong);
  color: var(--ink);
  transform: translateY(-200%);
}
.skip-link:focus { transform: none; }

.topbar { display: none; }
.scrim { display: none; }

.rail {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  height: 100dvh;
  display: flex;
  flex-direction: column;
  background: var(--surface);
  border-right: 1px solid var(--line);
  min-width: 0;
}

.wordmark {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--ink);
  text-decoration: none;
  font-family: var(--font-display);
  font-stretch: 112%;
  font-size: 1.1875rem;
  font-weight: 750;
  letter-spacing: -0.02em;
  line-height: 1;
}
.wordmark svg { width: 30px; height: 24px; flex: none; }
.wordmark__box { fill: var(--surface); stroke: var(--ink); stroke-width: 1.5; }
.wordmark__wire { fill: none; stroke: var(--ink); stroke-width: 1.5; }
.wordmark__dot { fill: var(--ok); }

.rail__head { padding: var(--s5) var(--s5) var(--s4); }

.rail__progress { padding: 0 var(--s5) var(--s4); }
.rail__progress-row {
  display: flex; justify-content: space-between; align-items: baseline;
  margin-bottom: 6px;
}
.rail__progress-row .mono { font-size: var(--fs-xs); color: var(--ink); }

.rail__scroll {
  flex: 1 1 auto;
  overflow-y: auto;
  overscroll-behavior: contain;
  padding: 0 var(--s3) var(--s5);
  border-top: 1px solid var(--line);
  scrollbar-width: thin;
  scrollbar-color: var(--line-strong) transparent;
}

.rail-module { padding-top: var(--s4); }
.rail-module__head {
  display: flex; align-items: baseline; gap: var(--s2);
  padding: 0 var(--s3) 6px;
}
.rail-module__code { color: var(--ink); }
.rail-module__title { font-family: var(--font-display); font-size: var(--fs-sm); font-weight: 700; color: var(--ink); line-height: 1.25; }
.rail-module__count { margin-left: auto; font-size: var(--fs-micro); color: var(--ink-2); white-space: nowrap; }

.rail-lesson {
  display: grid;
  grid-template-columns: 26px minmax(0, 1fr) 12px;
  align-items: center;
  gap: var(--s2);
  padding: 6px var(--s3);
  border-radius: var(--radius);
  color: var(--ink-2);
  font-size: var(--fs-sm);
  line-height: 1.3;
  text-decoration: none;
  position: relative;
}
.rail-lesson:hover { background: var(--surface-2); color: var(--ink); }
.rail-lesson__code { font-size: var(--fs-micro); color: var(--ink-2); white-space: nowrap; }
.rail-lesson__title { min-width: 0; }
.rail-lesson[aria-current="page"] { background: var(--surface-2); color: var(--ink); font-weight: 600; }
.rail-lesson[aria-current="page"]::before {
  content: "";
  position: absolute; left: 0; top: 0; bottom: 0;
  width: 2px;
  background: var(--accent);
}
.rail-lesson[aria-current="page"] .rail-lesson__code { color: var(--ink); }
.rail-soon { padding: 4px var(--s3) 6px; font-size: var(--fs-sm); color: var(--ink-2); }

/* done box: an empty square until the lesson is done, then a ticked one */
.done-box {
  display: grid; place-items: center;
  width: 12px; height: 12px; flex: none;
  border: 1px solid var(--line-strong);
  border-radius: 1px;
  font-size: 10px;
  color: var(--on-accent);
}
.done-box.is-done { background: var(--accent); border-color: var(--accent); }
.done-box .icon { stroke-width: 2.4; }

.rail__foot {
  display: flex; align-items: center; justify-content: space-between; gap: var(--s2);
  padding: var(--s3);
  border-top: 1px solid var(--line);
}
.rail__foot .btn { min-width: 0; }
.rail__foot .btn[aria-current="page"] { color: var(--ink); background: var(--surface-2); }

.main { min-width: 0; }
.view {
  --gutter: clamp(16px, 4vw, 48px);
  max-width: calc(var(--content-w) + 2 * var(--gutter));
  padding: var(--s6) var(--gutter) var(--s8);
}

/* below 860px the rail becomes a drawer under a top bar */
@media (max-width: 859.98px) {
  .app { display: block; }

  .topbar {
    position: sticky; top: 0; z-index: 30;
    display: flex; align-items: center; justify-content: space-between;
    height: var(--bar-h);
    padding: 0 var(--s2) 0 var(--s4);
    background: var(--surface);
    border-bottom: 1px solid var(--line);
  }
  .topbar .wordmark { font-size: 1.0625rem; }
  .topbar .wordmark svg { width: 26px; height: 21px; }
  .topbar__right { display: flex; align-items: center; gap: var(--s2); }
  .topbar__pct { font-size: var(--fs-xs); color: var(--ink-2); }

  .rail {
    position: fixed;
    top: var(--bar-h); left: 0; right: 0;
    z-index: 29;
    height: auto;
    max-height: calc(100dvh - var(--bar-h));
    border-right: 0;
    border-bottom: 1px solid var(--line);
    box-shadow: var(--shadow-float);
    display: none;
  }
  .rail__head { display: none; }
  .rail__progress { padding-top: var(--s4); }
  .app.is-menu-open .rail { display: flex; }
  .app.is-menu-open .scrim {
    display: block;
    position: fixed; inset: var(--bar-h) 0 0 0;
    z-index: 28;
    background: var(--scrim);
    border: 0; padding: 0; border-radius: 0;
  }
  .rail-lesson { min-height: 40px; }
  .view { padding-top: var(--s4); padding-bottom: var(--s7); }
}

/* ---- 5. Home ------------------------------------------------------------ */

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 460px);
  gap: var(--s6);
  align-items: center;
  padding-bottom: var(--s6);
}
.hero__text { display: grid; gap: var(--s4); min-width: 0; }
.hero__title {
  font-family: var(--font-display);
  font-stretch: 108%;
  font-size: var(--fs-xl);
  font-weight: 750;
  letter-spacing: -0.025em;
  line-height: 1.04;
  max-width: 16ch;
}
.hero__lede { font-size: var(--fs-md); color: var(--ink-2); max-width: 38ch; line-height: 1.4; }
.hero__cta { display: flex; flex-wrap: wrap; align-items: center; gap: var(--s4); margin-top: var(--s1); }
.hero__cta .btn { min-height: 44px; padding-inline: 18px; font-size: 0.9375rem; }
.hero__next { display: grid; gap: 2px; font-size: var(--fs-sm); color: var(--ink-2); min-width: 0; }
.hero__next strong { color: var(--ink); font-weight: 600; }

/* the hero drawing: one request path, in the four request shapes */
.hero__fig { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: var(--s3); }
.hero__fig { display: grid; gap: var(--s2); }
.hero__fig > svg { width: 100%; height: auto; }
.hero__fig .sm-legend { border: 0; padding: 0 var(--s1); justify-self: center; background: transparent; }
.fig-box { fill: var(--surface); stroke: var(--ink); stroke-width: 1.25; }
.fig-box--soft { fill: var(--surface-2); }
.fig-wire { fill: none; stroke: var(--ink-2); stroke-width: 1; }
.fig-wire--flow { stroke-dasharray: 3 5; animation: sm-flow 1.6s linear infinite; }
.fig-label { font-family: var(--font-mono); font-size: 10.5px; font-weight: 500; fill: var(--ink); letter-spacing: 0.04em; }
.fig-label--quiet { fill: var(--ink-2); }
.fig-ok { fill: var(--ok); }
.fig-slow { fill: var(--slow); }
.fig-cached { fill: none; stroke: var(--cached); stroke-width: 1.75; }
.fig-fail { fill: none; stroke: var(--fail); stroke-width: 1.75; stroke-linecap: round; }
.fig-bar { fill: var(--line); }
.fig-bar--on { fill: var(--accent); }
@keyframes sm-flow { to { stroke-dashoffset: -16; } }

.home-progress { display: grid; gap: var(--s2); padding: var(--s4) 0 var(--s5); border-top: 1px solid var(--line-strong); }
.home-progress__meta { display: flex; flex-wrap: wrap; gap: var(--s2) var(--s5); font-size: var(--fs-xs); color: var(--ink-2); }
.home-progress__meta b { color: var(--ink); font-weight: 500; }

/* a module is a parts list: one header row, then a cell per lesson */
.module { padding: var(--s5) 0 var(--s4); border-top: 1px solid var(--line-strong); }
.module__head {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: baseline;
  gap: var(--s2) var(--s4);
  padding-bottom: var(--s4);
}
.module__code { font-family: var(--font-mono); font-size: var(--fs-sm); font-weight: 600; color: var(--ink); }
.module__title {
  font-family: var(--font-display);
  font-size: var(--fs-lg);
  font-weight: 700;
  letter-spacing: -0.015em;
  display: inline;
}
.module__tagline { display: inline; margin-left: var(--s3); font-size: 0.9375rem; color: var(--ink-2); }
.module__count { font-size: var(--fs-xs); color: var(--ink-2); white-space: nowrap; }

.module__lessons {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(min(100%, 232px), 1fr));
  gap: 1px;
  padding: 1px;
}
.module__lessons > li { box-shadow: 0 0 0 1px var(--line); }
.lesson-cell {
  display: grid;
  grid-template-columns: 30px minmax(0, 1fr) 12px;
  align-items: center;
  gap: var(--s3);
  min-height: 52px;
  height: 100%;
  padding: var(--s2) var(--s3);
  background: var(--surface);
  color: var(--ink);
  font-size: 0.9375rem;
  font-weight: 500;
  line-height: 1.25;
  text-decoration: none;
  transition: background-color 0.12s;
}
a.lesson-cell:hover { background: var(--accent-soft); }
a.lesson-cell:focus-visible { outline-offset: -2px; }
.lesson-cell__code { font-size: var(--fs-xs); color: var(--ink-2); }
.lesson-cell--soon { color: var(--ink-2); font-weight: 400; }

.home-foot {
  display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: var(--s3);
  padding-top: var(--s5);
  border-top: 1px solid var(--line-strong);
}

@media (max-width: 720px) {
  .hero { grid-template-columns: minmax(0, 1fr); gap: var(--s5); padding-bottom: var(--s5); }
  .module__head { grid-template-columns: auto minmax(0, 1fr) auto; }
  .module__tagline { display: block; margin: 2px 0 0; }
}

/* ---- 6. Lesson page ----------------------------------------------------- */

/* the header is a drawing-sheet title block: code | title and idea | status */
.lesson-head {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  background: var(--surface);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
}
.lesson-head__cell { padding: var(--s3) var(--s4); min-width: 0; }
.lesson-head__id { grid-column: 1; grid-row: 1; display: grid; align-content: center; gap: 2px; }
.lesson-head__main { grid-column: 2; grid-row: 1; border-left: 1px solid var(--line); }
.lesson-head__meta { grid-column: 3; grid-row: 1; border-left: 1px solid var(--line); }
.lesson-head__code { font-family: var(--font-mono); font-size: var(--fs-lg); font-weight: 600; letter-spacing: -0.03em; line-height: 1; color: var(--ink); }
.lesson-head__main { display: grid; gap: 6px; align-content: center; }
.lesson-head__title {
  font-family: var(--font-display);
  font-stretch: 106%;
  font-size: clamp(1.5rem, 1.25rem + 1vw, 2rem);
  font-weight: 750;
  letter-spacing: -0.022em;
  line-height: 1.06;
}
.lesson-head__idea {
  font-size: var(--fs-md);
  line-height: 1.35;
  color: var(--ink-2);
  max-width: 52ch;
}
.lesson-head__meta { display: grid; align-content: center; justify-items: end; gap: 6px; font-size: var(--fs-xs); color: var(--ink-2); white-space: nowrap; }
.lesson-head__done { display: inline-flex; align-items: center; gap: 6px; color: var(--ink); font-weight: 500; }

@media (max-width: 640px) {
  .lesson-head { grid-template-columns: minmax(0, 1fr) auto; }
  .lesson-head__id { grid-template-columns: auto auto; justify-content: start; align-items: baseline; gap: var(--s3); padding-block: var(--s2); border-bottom: 1px solid var(--line); }
  .lesson-head__code { font-size: var(--fs-md); }
  .lesson-head__meta { grid-column: 2; grid-auto-flow: column; align-items: center; gap: var(--s3); padding-block: var(--s2); border-bottom: 1px solid var(--line); border-left: 0; }
  .lesson-head__main { grid-column: 1 / -1; grid-row: 2; border-left: 0; }
  .lesson-head__idea { font-size: var(--fs-base); }
}

.lesson-body { display: flex; flex-direction: column; min-width: 0; counter-reset: sec; }
.lesson-body > p { max-width: var(--measure); }

.lesson-section { padding: var(--s5) 0 var(--s2); min-width: 0; counter-increment: sec; }
.lesson-section__head {
  display: flex;
  align-items: center;
  gap: var(--s3);
  margin-bottom: var(--s4);
}
/* the rule that runs from the title to the edge of the sheet */
.lesson-section__head::after { content: ""; flex: 1 1 24px; height: 1px; background: var(--line-strong); }
.lesson-section__title {
  font-family: var(--font-display);
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.015em;
  min-width: 0;
}
.lesson-section__title:empty { display: none; }
.lesson-section__body { display: flex; flex-direction: column; gap: var(--s4); min-width: 0; }

.kind-tag {
  display: inline-flex; align-items: center; gap: 6px;
  flex: none;
  padding: 4px 8px 4px 6px;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
  font-family: var(--font-mono);
  font-size: var(--fs-micro);
  font-weight: 500;
  line-height: 1.3;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--ink);
}
.kind-tag .icon { font-size: 0.75rem; }
/* the step number comes from the section's place in the lesson */
.lesson-body .kind-tag::before { content: counter(sec, decimal-leading-zero); color: var(--ink-2); }
.lesson-section--try .kind-tag, .lesson-section--keep .kind-tag { background: var(--ink); border-color: var(--ink); color: var(--bg); }
.lesson-body .lesson-section--try .kind-tag::before, .lesson-body .lesson-section--keep .kind-tag::before { color: inherit; opacity: 0.7; }

@media (max-width: 560px) {
  .lesson-section__head { flex-wrap: wrap; row-gap: var(--s2); }
  .lesson-section__head::after { order: 1; }
  .lesson-section__title { order: 2; flex: 1 1 100%; }
}

.lesson-foot {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
  gap: var(--s4);
  margin-top: var(--s6);
  padding-top: var(--s5);
  border-top: 1px solid var(--line-strong);
}
.lesson-foot__link {
  display: grid;
  gap: 2px;
  padding: var(--s3) var(--s4);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--ink);
  text-decoration: none;
  text-align: left;
  min-width: 0;
  transition: border-color 0.12s, background-color 0.12s;
}
.lesson-foot__link:hover { border-color: var(--ink-2); }
.lesson-foot__dir { display: inline-flex; align-items: center; gap: 6px; }
.lesson-foot__title { font-weight: 600; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.lesson-foot__title .mono { font-weight: 500; margin-right: var(--s2); }
@media (max-width: 560px) {
  .lesson-foot__title { white-space: normal; text-wrap: balance; font-size: var(--fs-sm); line-height: 1.3; }
}
.lesson-foot__link--next { text-align: right; background: var(--accent); border-color: var(--accent); color: var(--on-accent); }
.lesson-foot__link--next:hover { background: var(--accent-hover); border-color: var(--accent-hover); }
.lesson-foot__link--next .micro { color: inherit; }
.lesson-foot__link--next .lesson-foot__dir { justify-content: flex-end; }

.error-card {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: var(--s3);
  margin-top: var(--s4);
  padding: var(--s4);
  border: 1px solid var(--fail);
  border-radius: var(--radius);
  background: var(--surface);
}
.error-card > .icon { color: var(--fail); font-size: 1.25rem; margin-top: 2px; }
.error-card__title { font-weight: 600; }
.error-card__msg { font-size: var(--fs-sm); color: var(--ink-2); white-space: pre-wrap; margin-top: var(--s1); }

/* the panel a stub lesson shows until its author replaces it */
.stub {
  display: grid; gap: var(--s2); justify-items: start;
  padding: var(--s5);
  border: 1px dashed var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
}
.stub__title { font-family: var(--font-display); font-size: var(--fs-md); font-weight: 700; }

/* ---- 7. Cheat sheet ----------------------------------------------------- */

.page-head { display: grid; gap: var(--s2); padding-bottom: var(--s5); }
.page-head__title {
  font-family: var(--font-display);
  font-stretch: 108%;
  font-size: var(--fs-xl);
  font-weight: 750;
  letter-spacing: -0.025em;
  line-height: 1.04;
}

.sheet { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: var(--s4); }
.sheet-card {
  display: flex; flex-direction: column;
  background: var(--surface);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  min-width: 0;
}
.sheet-card--wide { grid-column: 1 / -1; }
.sheet-card__head {
  display: flex; flex-wrap: wrap; align-items: baseline; justify-content: space-between; gap: 2px var(--s4);
  padding: var(--s3) var(--s4);
  border-bottom: 1px solid var(--line);
}
.sheet-card__title { font-family: var(--font-display); font-size: var(--fs-md); font-weight: 700; letter-spacing: -0.01em; }
.sheet-card__rule { font-size: var(--fs-sm); color: var(--ink-2); max-width: none; }
.sheet-card__fig { display: flex; flex-direction: column; gap: var(--s3); padding: var(--s4); min-width: 0; flex: 1 1 auto; }
.sheet-empty { display: flex; align-items: center; gap: var(--s2); padding: var(--s4) 0; font-size: var(--fs-sm); color: var(--ink-2); }
@media (max-width: 900px) { .sheet { grid-template-columns: minmax(0, 1fr); } }

/* horizontal bars on a shared log scale (latency ladder, downtime) */
.cs-bars { display: grid; gap: 6px; min-width: 0; }
.cs-bars__row { display: grid; grid-template-columns: minmax(0, 12.5rem) minmax(40px, 1fr) minmax(4.5rem, max-content); align-items: center; gap: var(--s3); min-height: 22px; }
.cs-bars__label { font-size: var(--fs-sm); line-height: 1.25; min-width: 0; }
.cs-bars__track { position: relative; height: 10px; border-left: 1px solid var(--line-strong); background: repeating-linear-gradient(90deg, transparent 0 calc(var(--decade, 12.5%) - 1px), var(--line) calc(var(--decade, 12.5%) - 1px) var(--decade, 12.5%)); }
.cs-bars__fill { position: absolute; left: 0; top: 2px; bottom: 2px; min-width: 2px; background: var(--ink); border-radius: 0 1px 1px 0; }
.cs-bars__row--accent .cs-bars__fill { background: var(--accent); }
.cs-bars__value { font-size: var(--fs-sm); text-align: right; white-space: nowrap; }
.cs-bars__group { margin-top: var(--s2); }
.cs-bars__group:first-child { margin-top: 0; }
.sheet-card--half .cs-bars__row { grid-template-columns: 4.75rem minmax(40px, 1fr) minmax(5rem, max-content); }
@media (max-width: 560px) {
  .cs-bars__row { grid-template-columns: minmax(0, 1fr) max-content; row-gap: 2px; }
  .cs-bars__track { grid-column: 1 / -1; grid-row: 2; }
  .sheet-card--half .cs-bars__row { grid-template-columns: 4.75rem minmax(40px, 1fr) max-content; }
  .sheet-card--half .cs-bars__track { grid-column: auto; grid-row: auto; }
}

/* a formula drawn as boxes with operators between them */
.cs-formula { display: flex; flex-wrap: wrap; align-items: stretch; gap: var(--s2); }
.cs-formula__box { display: grid; gap: 2px; align-content: center; padding: var(--s2) var(--s3); border: 1px solid var(--line-strong); border-radius: var(--radius); min-width: 0; }
.cs-formula__box--out { border-color: var(--ink); background: var(--accent-soft); }
.cs-formula__num { font-family: var(--font-mono); font-size: var(--fs-md); font-weight: 500; letter-spacing: -0.02em; line-height: 1.1; white-space: nowrap; }
.cs-formula__pair { display: inline-flex; align-items: stretch; gap: var(--s2); min-width: 0; }
.cs-formula__op { display: grid; place-items: center; font-family: var(--font-mono); font-size: var(--fs-md); color: var(--ink-2); }

/* building blocks: glyph, name, and the symptom that calls for it */
.cs-blocks { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 220px), 1fr)); gap: 1px; padding: 1px; }
.cs-block { box-shadow: 0 0 0 1px var(--line); display: grid; grid-template-columns: 32px minmax(0, 1fr); gap: 2px var(--s3); align-items: start; padding: var(--s3); background: var(--surface); }
.cs-block__glyph { grid-row: 1 / 3; display: grid; place-items: center; width: 32px; height: 32px; border: 1px solid var(--ink); border-radius: var(--radius); font-size: 1.125rem; }
.cs-block__name { font-weight: 600; font-size: 0.9375rem; line-height: 1.25; }
.cs-block__when { font-size: var(--fs-sm); color: var(--ink-2); line-height: 1.35; }

/* ---- 8. Widgets --------------------------------------------------------- */

.sm-label { display: block; font-size: var(--fs-sm); font-weight: 600; color: var(--ink); line-height: 1.3; }

/* slider: a fader on a hairline track */
.sm-slider { display: grid; gap: 0; min-width: 0; align-content: start; }
.sm-slider__head { display: flex; justify-content: space-between; align-items: baseline; gap: var(--s3); }
.sm-slider__head label { font-size: var(--fs-sm); font-weight: 600; line-height: 1.3; }
.sm-slider__value { font-family: var(--font-mono); font-variant-numeric: tabular-nums; font-size: var(--fs-sm); font-weight: 500; color: var(--ink); white-space: nowrap; }
.sm-slider input[type="range"] {
  -webkit-appearance: none;
  appearance: none;
  display: block;
  width: 100%;
  height: 40px;
  margin: 0;
  padding: 0;
  background: transparent;
  cursor: pointer;
  touch-action: pan-y;
  --track: linear-gradient(to right, var(--accent) var(--pct, 50%), var(--surface-2) var(--pct, 50%));
}
.sm-slider input[type="range"]::-webkit-slider-runnable-track {
  height: 6px;
  border-radius: 1px;
  background: var(--track);
  box-shadow: inset 0 0 0 1px var(--line-strong);
}
.sm-slider input[type="range"]::-moz-range-track {
  height: 6px;
  border-radius: 1px;
  background: var(--track);
  box-shadow: inset 0 0 0 1px var(--line-strong);
}
.sm-slider input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 12px;
  height: 24px;
  margin-top: -9px;
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  background: var(--surface);
}
.sm-slider input[type="range"]::-moz-range-thumb {
  width: 9px;
  height: 21px;
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  background: var(--surface);
}
.sm-slider input[type="range"]:focus-visible { outline: none; }
.sm-slider input[type="range"]:focus-visible::-webkit-slider-thumb { outline: 2px solid var(--accent); outline-offset: 2px; }
.sm-slider input[type="range"]:focus-visible::-moz-range-thumb { outline: 2px solid var(--accent); outline-offset: 2px; }
.sm-slider__scale { display: flex; justify-content: space-between; margin-top: -6px; font-family: var(--font-mono); font-size: var(--fs-micro); color: var(--ink-2); }

/* segmented */
.sm-seg-wrap { display: inline-grid; gap: 6px; min-width: 0; max-width: 100%; justify-items: start; }
.sm-seg {
  display: inline-flex;
  flex-wrap: wrap;
  max-width: 100%;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
}
.sm-seg__btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 6px;
  flex: 1 1 auto;
  min-height: 36px;
  padding: 4px 12px;
  border: 0;
  border-radius: 0;
  background: transparent;
  box-shadow: -1px 0 0 var(--line), 0 -1px 0 var(--line);
  color: var(--ink-2);
  font-size: var(--fs-sm);
  font-weight: 500;
  line-height: 1.2;
  white-space: nowrap;
}
.sm-seg { overflow: hidden; }
.sm-seg__btn:hover { color: var(--ink); background: var(--surface-2); }
.sm-seg__btn[aria-checked="true"] { background: var(--ink); color: var(--bg); font-weight: 600; box-shadow: none; }
.sm-seg__btn:focus-visible { outline-offset: -3px; }
.sm-seg__btn[aria-checked="true"]:focus-visible { outline-color: var(--bg); }

/* toggle: a slide switch with a square thumb */
.sm-toggle {
  display: inline-flex; align-items: center; gap: 10px;
  min-height: 40px;
  padding: 4px 0;
  border: 0;
  background: transparent;
  font-size: 0.9375rem;
  font-weight: 500;
  line-height: 1.25;
  text-align: left;
}
.sm-toggle__track {
  position: relative;
  width: 38px; height: 20px; flex: none;
  border-radius: var(--radius);
  border: 1px solid var(--ink-2);
  background: var(--surface);
  transition: background-color 0.15s, border-color 0.15s;
}
.sm-toggle__thumb {
  position: absolute; top: 3px; left: 3px;
  width: 12px; height: 12px;
  border-radius: 1px;
  background: var(--ink-2);
  transition: transform 0.15s, background-color 0.15s;
}
.sm-toggle[aria-checked="true"] .sm-toggle__track { background: var(--accent); border-color: var(--accent); }
.sm-toggle[aria-checked="true"] .sm-toggle__thumb { transform: translateX(18px); background: var(--on-accent); }
.sm-toggle__state { font-family: var(--font-mono); font-size: var(--fs-micro); color: var(--ink-2); letter-spacing: 0.06em; text-transform: uppercase; min-width: 3ch; }

/* stepper: minus, number, plus */
.sm-stepper { display: inline-grid; gap: 6px; min-width: 0; justify-items: start; }
.sm-stepper__row {
  display: inline-flex; align-items: stretch;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
}
.sm-stepper__btn {
  display: grid; place-items: center;
  width: 40px; min-height: 40px;
  border: 0; border-radius: 0;
  background: transparent;
  color: var(--ink);
  font-size: 1rem;
}
.sm-stepper__btn:hover { background: var(--surface-2); }
.sm-stepper__btn[aria-disabled="true"] { color: var(--line-strong); cursor: not-allowed; background: transparent; }
.sm-stepper__btn:focus-visible { outline-offset: -3px; }
.sm-stepper__value {
  display: grid; place-items: center;
  min-width: 4.5ch;
  padding: 0 var(--s3);
  border-inline: 1px solid var(--line);
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: var(--fs-md);
  font-weight: 500;
  white-space: nowrap;
}

/* compare */
.sm-compare { display: grid; gap: var(--s3); min-width: 0; }
.sm-compare__tabs { display: none; }
.sm-compare__panes { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: var(--s4); min-width: 0; }
.sm-compare__pane { display: flex; flex-direction: column; gap: var(--s2); min-width: 0; margin: 0; }
.sm-compare__label { display: flex; align-items: center; gap: var(--s2); }
.sm-compare__label b { display: inline-grid; place-items: center; width: 18px; height: 18px; border: 1px solid var(--ink); border-radius: var(--radius); color: var(--ink); font-weight: 600; letter-spacing: 0; }
.sm-compare__pane--after .sm-compare__label b { background: var(--ink); color: var(--bg); }
.sm-compare__content { min-width: 0; flex: 1 1 auto; }
.sm-compare.is-tabbed .sm-compare__tabs { display: block; }
.sm-compare.is-tabbed .sm-compare__panes { grid-template-columns: minmax(0, 1fr); }
.sm-compare.is-tabbed .sm-compare__pane { grid-area: 1 / 1; }
.sm-compare.is-tabbed .sm-compare__pane.is-off { visibility: hidden; }
.sm-compare.is-tabbed .sm-compare__label { display: none; }
.sm-compare__notes {
  display: grid; gap: var(--s2);
  padding: var(--s3) var(--s4);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
}
.sm-compare__notes ul { display: grid; gap: 4px; }
.sm-compare__notes li { display: grid; grid-template-columns: 16px minmax(0, 1fr); gap: var(--s2); font-size: 0.9375rem; line-height: 1.4; }
.sm-compare__notes li .icon { margin-top: 4px; color: var(--ink-2); font-size: 0.8125rem; }

/* quiz */
.sm-quiz { display: grid; gap: var(--s3); min-width: 0; }
.sm-quiz__q { font-size: var(--fs-md); font-weight: 600; line-height: 1.3; }
.sm-quiz__options { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 180px), 1fr)); gap: var(--s2); }
.sm-quiz__opt {
  position: relative;
  display: flex; flex-direction: column; align-items: stretch; justify-content: center; gap: var(--s2);
  min-height: 48px;
  padding: 10px 14px;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
  font-size: 0.9375rem;
  font-weight: 500;
  line-height: 1.3;
  text-align: left;
  min-width: 0;
  transition: border-color 0.12s, background-color 0.12s;
}
.sm-quiz__opt:hover:not([aria-disabled="true"]) { background: var(--accent-soft); border-color: var(--ink-2); }
.sm-quiz__opt[aria-disabled="true"] { cursor: default; }
.sm-quiz__mark {
  display: none;
  align-items: center; gap: 4px;
  font-family: var(--font-mono);
  font-size: var(--fs-micro);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}
.sm-quiz__opt.is-correct, .sm-quiz__opt.is-wrong { padding: 9px 13px; border-width: 2px; }
.sm-quiz__opt.is-correct { border-color: var(--ok); background: var(--ok-soft); }
.sm-quiz__opt.is-wrong { border-color: var(--fail); border-style: dashed; }
.sm-quiz__opt.is-correct .sm-quiz__mark, .sm-quiz__opt.is-wrong .sm-quiz__mark { display: inline-flex; }
.sm-quiz__opt.is-correct .sm-quiz__mark .icon { color: var(--ok); font-size: 0.875rem; }
.sm-quiz__opt.is-wrong .sm-quiz__mark .icon { color: var(--fail); font-size: 0.875rem; }
.sm-quiz[data-state="passed"] .sm-quiz__opt:not(.is-correct) { opacity: 0.55; }
.sm-quiz__opt.is-shaking { animation: sm-shake 0.3s ease; }
.sm-feedback {
  display: grid; grid-template-columns: auto minmax(0, 1fr); gap: var(--s2);
  padding: var(--s3) var(--s4);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  font-size: 0.9375rem;
  line-height: 1.4;
  max-width: none;
}
.sm-feedback:empty { display: none; }
.sm-feedback .icon { margin-top: 3px; font-size: 1rem; }
.sm-feedback.is-good { border-color: var(--ok); }
.sm-feedback.is-good .icon { color: var(--ok); }
.sm-feedback.is-bad .icon { color: var(--fail); }
@keyframes sm-shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-4px); }
  75% { transform: translateX(4px); }
}

/* order: put the rows in sequence */
.sm-order { display: grid; gap: var(--s3); min-width: 0; }
.sm-order__q { font-size: var(--fs-md); font-weight: 600; line-height: 1.3; }
.sm-order__list { display: grid; gap: var(--s2); position: relative; }
.sm-order__item {
  display: grid;
  grid-template-columns: 22px 28px minmax(0, 1fr) auto 40px 40px;
  align-items: center;
  gap: var(--s2);
  min-height: 48px;
  padding: 3px 3px 3px var(--s3);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
  touch-action: pan-y;
}
.sm-order__pos { grid-column: 1; }
.sm-order__grip { grid-column: 2; }
.sm-order__label { grid-column: 3; }
.sm-order__mark { grid-column: 4; }
.sm-order__up { grid-column: 5; }
.sm-order__down { grid-column: 6; }
.sm-order__item > * { grid-row: 1; }
.sm-order__pos { font-family: var(--font-mono); font-size: var(--fs-sm); color: var(--ink-2); }
.sm-order__grip {
  display: grid; place-items: center;
  width: 28px; height: 40px;
  color: var(--ink-2);
  cursor: grab;
  touch-action: none;
}
.sm-order__label { font-size: 0.9375rem; font-weight: 500; line-height: 1.3; min-width: 0; }
.sm-order__mark { display: inline-flex; align-items: center; gap: 4px; font-family: var(--font-mono); font-size: var(--fs-micro); letter-spacing: 0.06em; text-transform: uppercase; white-space: nowrap; }
.sm-order__mark:empty { display: none; }
.sm-order__item.is-right .sm-order__mark .icon { color: var(--ok); font-size: 0.875rem; }
.sm-order__item.is-wrong .sm-order__mark .icon { color: var(--fail); font-size: 0.875rem; }
.sm-order__item.is-right { border-color: var(--ok); }
.sm-order__item.is-wrong { border-color: var(--fail); border-style: dashed; }
.sm-order__move {
  display: grid; place-items: center;
  width: 40px; height: 40px;
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--ink);
  font-size: 1rem;
}
.sm-order__move:hover:not([aria-disabled="true"]) { background: var(--surface-2); border-color: var(--ink-2); }
.sm-order__move[aria-disabled="true"] { color: var(--line-strong); cursor: not-allowed; }
.sm-order__item.is-dragging { z-index: 2; border-color: var(--ink); box-shadow: var(--shadow-float); cursor: grabbing; }
.sm-order__item.is-dragging .sm-order__grip { cursor: grabbing; }
.sm-order[data-state="passed"] .sm-order__grip, .sm-order[data-state="passed"] .sm-order__move { visibility: hidden; }
.sm-order__foot { display: flex; flex-wrap: wrap; align-items: center; gap: var(--s3); }
.sm-order__foot .sm-feedback { flex: 1 1 240px; }
@media (max-width: 480px) {
  .sm-order__item { grid-template-columns: 16px 24px minmax(0, 1fr) 40px 40px; column-gap: 6px; padding-left: var(--s2); }
  .sm-order__grip { width: 24px; }
  .sm-order__mark { grid-column: 3 / -1; grid-row: 2; padding-bottom: 4px; }
  .sm-order__up { grid-column: 4; }
  .sm-order__down { grid-column: 5; }
}

/* challenge */
.sm-challenge {
  display: grid;
  border: 1px solid var(--ink);
  border-radius: var(--radius);
  background: var(--surface);
  min-width: 0;
}
.sm-challenge__banner {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: center;
  gap: var(--s3);
  padding: var(--s3) var(--s4);
  border-bottom: 1px solid var(--line);
}
.sm-challenge__icon {
  display: grid; place-items: center;
  width: 32px; height: 32px;
  border-radius: var(--radius);
  border: 1px solid var(--ink);
  color: var(--ink);
  font-size: 1rem;
}
.sm-challenge__goal { font-weight: 600; line-height: 1.3; max-width: none; }
.sm-challenge__hint {
  display: grid; grid-template-columns: auto minmax(0, 1fr); gap: var(--s2);
  padding: var(--s3) var(--s4);
  border-bottom: 1px solid var(--line);
  background: var(--surface-2);
  font-size: 0.9375rem;
  max-width: none;
}
.sm-challenge__hint .icon { margin-top: 4px; color: var(--ink-2); }
.sm-challenge__body { display: flex; flex-direction: column; gap: var(--s4); padding: var(--s4); min-width: 0; }
.sm-challenge__body:empty { display: none; }
.sm-challenge__foot {
  display: grid;
  grid-template-columns: minmax(80px, 200px) minmax(0, 1fr);
  align-items: center;
  gap: var(--s4);
  padding: var(--s3) var(--s4);
  border-top: 1px solid var(--line);
}
.sm-challenge__status { display: flex; align-items: flex-start; gap: var(--s2); font-size: var(--fs-sm); color: var(--ink); max-width: none; }
.sm-challenge__status .icon { margin-top: 3px; font-size: 0.875rem; }
.sm-challenge__status-icon:empty { display: none; }
.sm-challenge[data-state="passed"] { border-color: var(--ok); box-shadow: inset 0 0 0 1px var(--ok); }
.sm-challenge[data-state="passed"] .sm-challenge__icon { background: var(--ok); border-color: var(--ok); color: var(--surface); }
.sm-challenge[data-state="passed"] .sm-meter__seg.is-on { background: var(--ok); border-color: var(--ok); }
.sm-challenge[data-state="passed"] .sm-challenge__status { font-weight: 600; }
.sm-challenge[data-state="passed"] .sm-challenge__status .icon { color: var(--ok); }
.sm-challenge[data-state="failed"] { border-color: var(--fail); border-style: dashed; }
.sm-challenge[data-state="failed"] .sm-challenge__icon { border-color: var(--fail); color: var(--fail); }
.sm-challenge[data-state="failed"] .sm-challenge__status .icon { color: var(--fail); }
.sm-challenge[data-state="failed"] .sm-challenge__status { font-weight: 600; }
@media (max-width: 560px) {
  .sm-challenge__foot { grid-template-columns: minmax(0, 1fr); gap: var(--s2); }
  .sm-challenge__banner { padding-inline: var(--s3); }
  .sm-challenge__body { padding-inline: var(--s3); }
}

/* code block */
.sm-code {
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
  overflow: hidden;
  min-width: 0;
}
.sm-code__bar {
  display: flex; align-items: center; justify-content: space-between; gap: var(--s2);
  padding: 4px;
  border-bottom: 1px solid var(--line);
  background: var(--surface-2);
}
.sm-code__tabs { display: flex; flex-wrap: wrap; gap: 2px; min-width: 0; }
.sm-code__tab {
  min-height: 30px;
  padding: 5px 10px;
  border: 1px solid transparent;
  background: transparent;
  color: var(--ink-2);
  font-family: var(--font-mono);
  font-size: var(--fs-xs);
  font-weight: 500;
}
.sm-code__tab:hover { color: var(--ink); }
.sm-code__tab[aria-selected="true"] { background: var(--surface); border-color: var(--line-strong); color: var(--ink); font-weight: 600; }
span.sm-code__tab { display: inline-flex; align-items: center; cursor: default; background: transparent; border-color: transparent; }
.sm-code pre {
  margin: 0;
  padding: var(--s4);
  overflow: auto;
  max-height: 420px;
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  font-variant-ligatures: none;
  line-height: 1.6;
  tab-size: 2;
  color: var(--ink);
  white-space: pre;
  overflow-wrap: normal;
}
.sm-code pre:focus-visible { outline-offset: -2px; }
.sm-code .tok-c { color: var(--ink-2); font-style: italic; }
.sm-code .tok-s { color: var(--accent); }
.sm-code .tok-n { font-weight: 600; }
@media (max-width: 859.98px), (pointer: coarse) { .sm-code__tab, .sm-seg__btn { min-height: 40px; } }

/* glossary term */
.sm-term { position: relative; display: inline; }
.sm-term__btn {
  display: inline;
  padding: 0; margin: 0;
  border: 0;
  border-radius: 0;
  background: transparent;
  font: inherit;
  color: inherit;
  text-decoration: underline dotted var(--ink-2);
  text-decoration-thickness: 1.5px;
  text-underline-offset: 0.22em;
  cursor: help;
}
.sm-term__btn:hover, .sm-term.is-open .sm-term__btn { text-decoration-color: var(--accent); text-decoration-style: solid; }
.sm-term__pop {
  display: none;
  position: absolute;
  top: calc(100% + 6px); left: 0;
  z-index: 40;
  width: max-content;
  max-width: min(280px, calc(100vw - 32px));
  padding: 10px 12px;
  border: 1px solid var(--ink);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: var(--shadow-float);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: var(--fs-sm);
  font-weight: 400;
  font-style: normal;
  letter-spacing: 0;
  line-height: 1.45;
  text-transform: none;
  text-align: left;
  white-space: normal;
}
.sm-term.is-open .sm-term__pop { display: block; }
.sm-term__pop strong { display: block; font-weight: 600; margin-bottom: 2px; }

/* toast */
.sm-toasts {
  position: fixed;
  left: 50%; bottom: max(24px, env(safe-area-inset-bottom));
  transform: translateX(-50%);
  z-index: 90;
  display: grid; justify-items: center; gap: var(--s2);
  width: max-content;
  max-width: calc(100vw - 32px);
  pointer-events: none;
}
.sm-toast {
  display: inline-flex; align-items: center; gap: var(--s2);
  padding: 10px 14px;
  border-radius: var(--radius);
  background: var(--ink);
  color: var(--bg);
  box-shadow: var(--shadow-float);
  font-size: 0.875rem;
  font-weight: 500;
  animation: sm-toast-in 0.18s ease;
}
.sm-toast.is-leaving { opacity: 0; transition: opacity 0.2s; }
@keyframes sm-toast-in {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: none; }
}

/* stat: one live reading, like a gauge on a panel */
.sm-stat { display: grid; gap: 4px; align-content: start; min-width: 0; padding: var(--s3) var(--s4); background: var(--surface); }
.sm-stat__value { display: flex; align-items: baseline; gap: 4px; font-family: var(--font-mono); font-variant-numeric: tabular-nums; line-height: 1; white-space: nowrap; }
.sm-stat__value b { font-size: 1.625rem; font-weight: 500; letter-spacing: -0.04em; }
.sm-stat__value small { font-size: var(--fs-sm); color: var(--ink-2); }
.sm-stat .sm-state { font-size: var(--fs-xs); }
.sm-stat--sm .sm-stat__value b { font-size: var(--fs-md); }
:not(.sm-stats) > .sm-stat { border: 1px solid var(--line); border-radius: var(--radius); }

.sm-stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 132px), 1fr));
  gap: 1px;
  background: var(--line);
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  min-width: 0;
  overflow: hidden;
}
@media (max-width: 480px) {
  .sm-stats { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .sm-stats > .sm-stat:last-child:nth-child(odd) { grid-column: 1 / -1; }
  .sm-stat { padding: var(--s2) var(--s3); }
  .sm-stat__value b { font-size: 1.375rem; }
}

/* charts: line chart and histogram share a frame */
.sm-chart, .sm-hist {
  display: grid; gap: var(--s2);
  padding: var(--s3) var(--s3) var(--s2);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  min-width: 0;
  margin: 0;
}
.sm-chart__head { display: flex; flex-wrap: wrap; align-items: baseline; justify-content: space-between; gap: 4px var(--s4); }
.sm-chart__title { font-size: var(--fs-sm); font-weight: 600; line-height: 1.3; }
.sm-chart__legend { display: flex; flex-wrap: wrap; gap: 2px var(--s4); }
.sm-chart__key { display: inline-flex; align-items: center; gap: 6px; font-size: var(--fs-xs); color: var(--ink); white-space: nowrap; }
.sm-chart__key svg { width: 22px; height: 8px; flex: none; }
.sm-chart__key b { font-family: var(--font-mono); font-variant-numeric: tabular-nums; font-weight: 500; }
.sm-chart__plot { position: relative; min-width: 0; }
.sm-chart__plot > svg { width: 100%; height: 100%; overflow: visible; }
.sm-chart__grid { stroke: var(--line); stroke-width: 1; shape-rendering: crispEdges; }
.sm-chart__axis { stroke: var(--line-strong); stroke-width: 1; shape-rendering: crispEdges; }
.sm-chart__tick { font-family: var(--font-mono); font-size: 10px; fill: var(--ink-2); }
.sm-chart__line { fill: none; stroke-width: 2; stroke-linejoin: round; stroke-linecap: round; }
.sm-chart__dot { stroke: var(--surface); stroke-width: 2; }
.sm-chart__limit { stroke: var(--ink); stroke-width: 1; stroke-dasharray: 5 4; shape-rendering: crispEdges; }
.sm-chart__limit-label { font-family: var(--font-mono); font-size: 10px; fill: var(--ink); paint-order: stroke; stroke: var(--surface); stroke-width: 3px; }
.sm-chart__cursor { stroke: var(--ink-2); stroke-width: 1; shape-rendering: crispEdges; }
.sm-chart__bar { fill: var(--ink-2); }
.sm-chart__marker { stroke-width: 1.5; shape-rendering: crispEdges; }
.sm-chart__marker-label { font-family: var(--font-mono); font-size: 10px; fill: var(--ink); paint-order: stroke; stroke: var(--surface); stroke-width: 3px; }
.sm-chart__empty { font-family: var(--font-mono); font-size: 11px; fill: var(--ink-2); }
.sm-chart__tip {
  position: absolute; top: 4px; z-index: 3;
  display: grid; gap: 2px;
  padding: 6px 8px;
  border: 1px solid var(--ink);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: var(--shadow-float);
  font-size: var(--fs-xs);
  white-space: nowrap;
  pointer-events: none;
}
/* series colours: used for strokes and fills only, never for text */
.sm-series--ink { stroke: var(--series-a); fill: var(--series-a); }
.sm-series--accent { stroke: var(--series-b); fill: var(--series-b); }
.sm-series--violet { stroke: var(--series-c); fill: var(--series-c); }
.sm-series--orange { stroke: var(--series-d); fill: var(--series-d); }
.sm-series--muted { stroke: var(--ink-2); fill: var(--ink-2); }
.sm-series--ok { stroke: var(--ok); fill: var(--ok); }
.sm-series--slow { stroke: var(--slow); fill: var(--slow); }
.sm-series--fail { stroke: var(--fail); fill: var(--fail); }
.sm-series--cached { stroke: var(--cached); fill: var(--cached); }
.sm-chart__line[class*="sm-series--"], .sm-chart__key path { fill: none; }

/* timeline: numbered stops on one wire */
.sm-timeline { display: grid; gap: var(--s3); min-width: 0; container-type: inline-size; }
.sm-timeline__list { display: flex; min-width: 0; }
.sm-timeline__item { flex: 1 1 0; min-width: 0; position: relative; }
.sm-timeline__item::before {
  content: "";
  position: absolute; top: 15px; left: 0; right: 0;
  height: 1px;
  background: var(--line-strong);
}
.sm-timeline__item:first-child::before { left: 50%; }
.sm-timeline__item:last-child::before { right: 50%; }
.sm-timeline__step {
  position: relative;
  display: grid; justify-items: center; gap: 6px;
  width: 100%;
  min-height: 40px;
  padding: 0 4px 4px;
  border: 0;
  background: transparent;
  color: var(--ink-2);
  font-size: var(--fs-sm);
  font-weight: 500;
  line-height: 1.25;
  text-align: center;
}
.sm-timeline__num {
  display: grid; place-items: center;
  width: 30px; height: 30px;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--ink);
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  font-weight: 500;
}
.sm-timeline__step:hover { color: var(--ink); }
.sm-timeline__step:hover .sm-timeline__num { border-color: var(--ink); }
.sm-timeline__item.is-past .sm-timeline__num { border-color: var(--ink); }
.sm-timeline__step[aria-current="step"] { color: var(--ink); font-weight: 600; }
.sm-timeline__step[aria-current="step"] .sm-timeline__num { background: var(--ink); border-color: var(--ink); color: var(--bg); }
.sm-timeline__step:focus-visible { outline-offset: 0; }
.sm-timeline__detail { padding: var(--s3) var(--s4); border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); font-size: 0.9375rem; line-height: 1.45; }
.sm-timeline__detail:empty { display: none; }
@container (max-width: 520px) {
  .sm-timeline__list { flex-direction: column; }
  .sm-timeline__item::before { top: 0; bottom: 0; left: 15px; right: auto; width: 1px; height: auto; }
  .sm-timeline__item:first-child::before { left: 15px; top: 50%; }
  .sm-timeline__item:last-child::before { right: auto; bottom: 50%; }
  .sm-timeline__step { grid-template-columns: 30px minmax(0, 1fr); justify-items: start; align-items: center; gap: var(--s3); padding: 5px 0; text-align: left; }
}

/* takeaway: the Keep card */
.sm-takeaway {
  display: grid;
  grid-template-columns: minmax(0, 1.5fr) minmax(0, 1fr);
  border: 1px solid var(--ink);
  border-radius: var(--radius);
  background: var(--surface);
  min-width: 0;
}
.sm-takeaway__block { display: grid; gap: var(--s2); align-content: start; padding: var(--s4); min-width: 0; }
.sm-takeaway__block--number { border-left: 1px solid var(--line); }
.sm-takeaway__block--say { grid-column: 1 / -1; border-top: 1px solid var(--line); background: var(--accent-soft); }
.sm-takeaway__block--code { grid-column: 1 / -1; border-top: 1px solid var(--line); padding: var(--s3); }
.sm-takeaway__text { max-width: none; }
.sm-takeaway__block--rule .sm-takeaway__text { font-family: var(--font-display); font-size: var(--fs-lg); font-weight: 700; letter-spacing: -0.015em; line-height: 1.2; text-wrap: balance; }
.sm-takeaway__block--number .sm-takeaway__text { font-family: var(--font-mono); font-variant-numeric: tabular-nums; font-size: var(--fs-md); font-weight: 500; letter-spacing: -0.02em; line-height: 1.3; }
.sm-takeaway__block--say .sm-takeaway__text { font-size: var(--fs-md); line-height: 1.4; max-width: 62ch; quotes: "\201C" "\201D"; }
.sm-takeaway__block--say .sm-takeaway__text::before { content: open-quote; }
.sm-takeaway__block--say .sm-takeaway__text::after { content: close-quote; }
@media (max-width: 640px) {
  .sm-takeaway { grid-template-columns: minmax(0, 1fr); }
  .sm-takeaway__block--number { border-left: 0; border-top: 1px solid var(--line); }
  .sm-takeaway__block { padding: var(--s3); }
  .sm-takeaway__block--rule .sm-takeaway__text { font-size: 1.25rem; }
}

/* legend: the four request shapes */
.sm-legend { display: inline-flex; flex-wrap: wrap; gap: var(--s2) var(--s4); padding: 6px var(--s3); border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); }

/* ---- 9. Motion and print ------------------------------------------------ */

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }
  .fig-wire--flow { animation: none; }
}

@media print {
  .rail, .topbar, .lesson-foot, .sm-toasts { display: none !important; }
  .app { display: block; }
  body { background-image: none; }
}