/* GRE Mathematics study site — see docs/DESIGN.md for the design plan this
   implements. Tokens first, then layout, then components. */

:root {
  --paper: #eef1ea;
  --paper-raised: #e4e9df;
  --ink: #16202a;
  --ink-dim: #4b5a63;
  --rule: #c9d1c4;
  --rule-strong: #a8b3a0;
  --signal: #6c4a96;
  --signal-ink: #ffffff;
  --amber: #b8792a;
  --brick: #a6433d;
  --focus: #4a2f73;
  --radius: 3px;
  --serif: "Literata", "Iowan Old Style", "Palatino Linotype", Georgia, serif;
  --mono: "IBM Plex Mono", ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  color-scheme: light;
  padding-top: env(safe-area-inset-top, 0px);
  padding-bottom: env(safe-area-inset-bottom, 0px);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #121a20;
    --paper-raised: #182129;
    --ink: #e7eae2;
    --ink-dim: #a9b6ae;
    --rule: #2a343a;
    --rule-strong: #3c4a52;
    --signal: #c2a2ea;
    --signal-ink: #17101f;
    --amber: #d9a45c;
    --brick: #e28a83;
    --focus: #ded0f7;
    color-scheme: dark;
  }
}

:root[data-theme="dark"] {
  --paper: #121a20;
  --paper-raised: #182129;
  --ink: #e7eae2;
  --ink-dim: #a9b6ae;
  --rule: #2a343a;
  --rule-strong: #3c4a52;
  --signal: #c2a2ea;
  --signal-ink: #17101f;
  --amber: #d9a45c;
  --brick: #e28a83;
  --focus: #ded0f7;
  color-scheme: dark;
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--paper);
  background-image:
    linear-gradient(var(--rule) 1px, transparent 1px),
    linear-gradient(90deg, var(--rule) 1px, transparent 1px);
  background-size: 28px 28px;
  background-attachment: local;
  color: var(--ink);
  font-family: var(--serif);
  font-size: 16px;
  line-height: 1.55;
}

img { max-width: 100%; }
[hidden] { display: none !important; }

a { color: var(--signal); }
a:not(.btn) { text-underline-offset: 3px; }

:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

.mono { font-family: var(--mono); }

/* Visually hidden but announced by screen readers — used for the single
   shared #live-region (drill feedback, exam submit confirmation). */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}
.num { font-family: var(--mono); font-variant-numeric: tabular-nums; }

/* ---------- layout shell ---------- */

.topbar {
  position: sticky;
  top: env(safe-area-inset-top, 0px);
  z-index: 10;
  display: flex;
  align-items: baseline;
  gap: 1.25rem;
  padding: 0.9rem 1.25rem;
  background: color-mix(in srgb, var(--paper) 92%, transparent);
  backdrop-filter: blur(6px);
  border-bottom: 1px solid var(--rule-strong);
  flex-wrap: wrap;
}

.brand {
  font-family: var(--serif);
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--ink);
  text-decoration: none;
  white-space: nowrap;
}

.topnav {
  display: flex;
  gap: 1rem;
  margin-left: auto;
  flex-wrap: wrap;
  align-items: baseline;
}

.topnav a {
  color: var(--ink-dim);
  text-decoration: none;
  font-family: var(--mono);
  font-size: 0.85rem;
}
.topnav a:hover, .topnav a.active { color: var(--signal); }

.theme-toggle {
  border: 1px solid var(--rule-strong);
  background: var(--paper-raised);
  color: var(--ink);
  font-family: var(--mono);
  font-size: 0.8rem;
  border-radius: var(--radius);
  padding: 0.3rem 0.55rem;
  cursor: pointer;
}
.theme-toggle:hover { border-color: var(--signal); }

main.view {
  max-width: 760px;
  margin: 0 auto;
  padding: 2rem 1.25rem 4rem;
}

h1, h2, h3 { font-family: var(--serif); line-height: 1.25; font-weight: 700; }
h1 { font-size: 1.7rem; margin: 0 0 0.35rem; }
h2 { font-size: 1.3rem; margin: 2rem 0 0.75rem; }
h3 { font-size: 1.05rem; margin: 1.25rem 0 0.5rem; }
p { margin: 0.75rem 0; max-width: 68ch; }
.blurb { color: var(--ink-dim); margin: 0 0 1.5rem; max-width: 60ch; }

.breadcrumb {
  font-family: var(--mono);
  font-size: 0.8rem;
  color: var(--ink-dim);
  margin-bottom: 0.5rem;
}
.breadcrumb a { color: var(--ink-dim); }

/* ---------- buttons & inputs ---------- */

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-family: var(--mono);
  font-size: 0.85rem;
  border: 1px solid var(--rule-strong);
  background: var(--paper-raised);
  color: var(--ink);
  padding: 0.5rem 0.9rem;
  border-radius: var(--radius);
  cursor: pointer;
  text-decoration: none;
  line-height: 1.2;
}
.btn:hover { border-color: var(--signal); color: var(--signal); }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }
.btn-primary {
  background: var(--signal);
  border-color: var(--signal);
  color: var(--signal-ink);
}
.btn-primary:hover { filter: brightness(1.08); color: var(--signal-ink); }
.btn-danger { border-color: var(--brick); color: var(--brick); }
.btn-danger:hover { background: var(--brick); color: var(--paper); }
.btn-row { display: flex; gap: 0.6rem; flex-wrap: wrap; margin-top: 1.25rem; }

input[type="text"], input[type="number"] {
  font-family: var(--mono);
  font-size: 1rem;
  padding: 0.5rem 0.6rem;
  border: 1px solid var(--rule-strong);
  border-radius: var(--radius);
  background: var(--paper);
  color: var(--ink);
}
input:focus-visible { outline: 2px solid var(--focus); outline-offset: 1px; }

/* ---------- curriculum spine (home + progress) ---------- */

.spine { border-top: 1px solid var(--rule-strong); margin-top: 1rem; }
.spine-row {
  display: grid;
  grid-template-columns: 2.4rem 1fr;
  gap: 0.9rem;
  padding: 1rem 0;
  border-bottom: 1px solid var(--rule);
  position: relative;
}
.spine-row.is-locked { opacity: 0.72; }
.spine-order {
  font-family: var(--mono);
  font-size: 0.85rem;
  color: var(--ink-dim);
  padding-top: 0.15rem;
}
.spine-main { min-width: 0; }
.spine-title-row { display: flex; align-items: baseline; gap: 0.6rem; flex-wrap: wrap; }
.spine-title {
  font-family: var(--serif);
  font-weight: 700;
  font-size: 1.1rem;
  text-decoration: none;
  color: var(--ink);
}
.spine-title:hover { color: var(--signal); }
.spine-prereq { font-size: 0.78rem; color: var(--ink-dim); font-family: var(--mono); }
.spine-blurb { color: var(--ink-dim); margin: 0.2rem 0 0.6rem; max-width: 56ch; }
.stat-line {
  display: grid;
  grid-template-columns: 4.3rem 1fr 3.4rem;
  align-items: center;
  gap: 0.6rem;
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--ink-dim);
  margin-top: 0.3rem;
  max-width: 26rem;
}
.trace {
  height: 6px;
  background: var(--rule);
  border-radius: 2px;
  overflow: hidden;
  position: relative;
}
.trace > span { display: block; height: 100%; background: var(--signal); }
.trace.amber > span { background: var(--amber); }
.spine-actions { margin-top: 0.6rem; display: flex; gap: 0.7rem; }
.spine-actions a { font-family: var(--mono); font-size: 0.78rem; }

/* ---------- lesson ---------- */

.lesson-meta { font-family: var(--mono); font-size: 0.8rem; color: var(--ink-dim); margin-bottom: 1.5rem; }
.section-kind {
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--signal);
  text-transform: lowercase;
  letter-spacing: 0.02em;
  margin: 0 0 0.35rem;
}
.lesson-section {
  padding: 1.1rem 0 1.1rem 1rem;
  border-left: 2px solid var(--rule);
  margin-bottom: 0.25rem;
}
.lesson-section[data-kind="discovery"] { border-left-color: var(--amber); }
.lesson-section[data-kind="formal"] { border-left-color: var(--signal); }
.lesson-section .md :first-child { margin-top: 0; }
.lesson-section .md :last-child { margin-bottom: 0; }
.lesson-section .md p { max-width: 66ch; }
.lesson-section .md strong { font-weight: 700; }
.lesson-svg { margin: 1rem 0; color: var(--ink); }
.lesson-svg svg { max-width: 100%; height: auto; display: block; }

.checkpoints { margin: 1.5rem 0 2rem; }
.checkpoint {
  border: 1px solid var(--rule-strong);
  border-radius: var(--radius);
  padding: 1rem;
  margin-bottom: 1rem;
  background: var(--paper-raised);
}
.checkpoint-label { font-family: var(--mono); font-size: 0.72rem; color: var(--ink-dim); margin-bottom: 0.5rem; }
.option-list { list-style: none; margin: 0.75rem 0 0; padding: 0; display: grid; gap: 0.5rem; }
.option-btn {
  display: flex;
  gap: 0.6rem;
  align-items: baseline;
  width: 100%;
  text-align: left;
  font-family: var(--serif);
  font-size: 0.98rem;
  background: var(--paper);
  border: 1px solid var(--rule-strong);
  border-radius: var(--radius);
  padding: 0.55rem 0.75rem;
  cursor: pointer;
  color: var(--ink);
}
.option-btn .opt-key { font-family: var(--mono); color: var(--ink-dim); }
.option-btn:hover:not(:disabled) { border-color: var(--signal); }
.option-btn.chosen { border-color: var(--signal); }
.option-btn:disabled { cursor: default; }
.option-btn.correct { border-color: var(--signal); background: color-mix(in srgb, var(--signal) 14%, var(--paper)); }
.option-btn.wrong { border-color: var(--brick); background: color-mix(in srgb, var(--brick) 12%, var(--paper)); }
.option-btn.correct-unchosen { border-color: var(--signal); border-style: dashed; }
.explain { margin-top: 0.75rem; font-size: 0.92rem; color: var(--ink-dim); }
.explain .md p:first-child { margin-top: 0; }

.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2.5rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--rule-strong);
  font-family: var(--mono);
  font-size: 0.85rem;
}
.lesson-nav a { text-decoration: none; }
.lesson-nav .nav-empty { color: var(--ink-dim); opacity: 0.5; }

/* ---------- drill / test / mock: single-question stage ---------- */

.stage-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  font-family: var(--mono);
  font-size: 0.8rem;
  color: var(--ink-dim);
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
  gap: 0.5rem;
}
.stage-timer { color: var(--ink); }
.stage-timer.low { color: var(--brick); }

.question-stage { max-width: 640px; margin: 0 auto; }
.prompt { font-size: 1.1rem; margin-bottom: 1.25rem; }
.prompt :first-child { margin-top: 0; }

.numeric-row { display: flex; gap: 0.6rem; align-items: center; margin: 1rem 0; flex-wrap: wrap; }
.numeric-row input { width: 12rem; }
.numeric-unit { font-family: var(--mono); color: var(--ink-dim); }
.feedback { margin: 1rem 0; padding: 0.85rem 1rem; border-radius: var(--radius); border: 1px solid var(--rule-strong); }
.feedback.correct { border-color: var(--signal); background: color-mix(in srgb, var(--signal) 12%, var(--paper)); }
.feedback.wrong { border-color: var(--brick); background: color-mix(in srgb, var(--brick) 10%, var(--paper)); }
.feedback-label { font-family: var(--mono); font-size: 0.78rem; margin-bottom: 0.4rem; }
.hint-box { margin: 0.75rem 0; font-size: 0.92rem; color: var(--ink-dim); }

.palette { display: flex; flex-wrap: wrap; gap: 0.4rem; margin: 1.25rem 0; }
.palette-cell {
  width: 2.1rem;
  height: 2.1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--mono);
  font-size: 0.8rem;
  border: 1px solid var(--rule-strong);
  border-radius: var(--radius);
  background: var(--paper-raised);
  color: var(--ink-dim);
  cursor: pointer;
}
.palette-cell.answered { color: var(--ink); border-color: var(--rule-strong); background: color-mix(in srgb, var(--signal) 10%, var(--paper-raised)); }
.palette-cell.marked::after { content: "•"; color: var(--amber); margin-left: 0.15rem; }
.palette-cell.review-wrong { border-color: var(--brick); }
.palette-cell.review-correct { border-color: var(--signal); }
/* Current-question ring uses outline (not border-color) so it always
   shows even when combined with .answered/.review-* border colors. */
.palette-cell.current { outline: 2px solid var(--signal); outline-offset: -2px; color: var(--signal); }

.session-summary { text-align: left; }
.summary-stat { font-family: var(--mono); font-size: 2rem; color: var(--ink); }
.summary-label { font-family: var(--mono); font-size: 0.8rem; color: var(--ink-dim); }

.review-item { border-top: 1px solid var(--rule); padding: 1rem 0; }
.review-item .verdict { font-family: var(--mono); font-size: 0.78rem; }
.review-item .verdict.correct { color: var(--signal); }
.review-item .verdict.wrong { color: var(--brick); }

/* ---------- progress page ---------- */

.progress-summary { display: flex; gap: 2rem; flex-wrap: wrap; margin-bottom: 2rem; }
.stat-block .summary-stat { display: block; }
.hist { display: grid; grid-template-columns: repeat(auto-fit, minmax(70px, 1fr)); gap: 0.75rem; margin: 1rem 0 2rem; max-width: 36rem; }
.hist-box { text-align: left; }
.hist-bar { height: 60px; background: var(--rule); border-radius: 2px; display: flex; align-items: flex-end; overflow: hidden; }
.hist-bar > span { display: block; width: 100%; background: var(--signal); }
.hist-label { font-family: var(--mono); font-size: 0.72rem; color: var(--ink-dim); margin-top: 0.3rem; }

.tag-list { list-style: none; margin: 0; padding: 0; max-width: 32rem; }
.tag-list li { display: flex; justify-content: space-between; gap: 1rem; padding: 0.4rem 0; border-bottom: 1px solid var(--rule); font-size: 0.92rem; }
.tag-list .tag-acc { font-family: var(--mono); color: var(--ink-dim); }
.missed-list li { display: block; }
.missed-list .missed-prompt { margin: 0 0 0.3rem; }
.missed-list .missed-prompt p { margin: 0; max-width: 60ch; }
.missed-list a { font-family: var(--mono); font-size: 0.82rem; }

.confirm-inline { border: 1px solid var(--brick); border-radius: var(--radius); padding: 0.85rem 1rem; margin-top: 0.75rem; max-width: 30rem; }
.confirm-inline p { margin: 0 0 0.6rem; }

.empty-note { color: var(--ink-dim); font-style: italic; }

.locked-note { font-family: var(--mono); font-size: 0.78rem; color: var(--brick); margin: 0.75rem 0; }

/* ---------- responsive ---------- */

@media (max-width: 480px) {
  main.view { padding: 1.25rem 1rem 3rem; }
  .stat-line { grid-template-columns: 3.6rem 1fr 3rem; }
  .spine-row { grid-template-columns: 1.8rem 1fr; }

  /* Header collapses to two rows: brand + toggle, then nav — instead of
     each nav link wrapping onto its own row. */
  .topbar { padding: 0.75rem 1rem; gap: 0.5rem 0.75rem; }
  .brand { order: 1; }
  .theme-toggle { order: 2; margin-left: auto; }
  .topnav {
    order: 3;
    flex-basis: 100%;
    margin-left: 0;
    gap: 0.9rem;
    flex-wrap: nowrap;
    overflow-x: auto;
  }
  .topnav a { padding: 0.25rem 0; white-space: nowrap; }
}

/* ---------- reduced motion ---------- */

@media (prefers-reduced-motion: reduce) {
  * { scroll-behavior: auto !important; }
}