/* ===========================================================
   VisualMath — shared stylesheet
   Light/dark via [data-theme] (set by js/theme.js), with a
   prefers-color-scheme fallback for no-JS / first paint.
   =========================================================== */

:root {
  --bg: #f5f7fa;
  --card: #ffffff;
  --page: #eef1f6;
  --text: #1b2330;
  --muted: #5c6675;
  --faint: #8b94a3;
  --border: #e3e8ef;
  --accent: #4f46e5;
  --accent-soft: #eef0fe;
  --accent-text: #3730a3;
  --teal: #0d9488;
  --teal-soft: #e2f5f0;
  --teal-text: #0f6e56;
  --amber-soft: #fdf2e0;
  --amber-text: #92500a;
  --good: #16a34a;
  --good-soft: #e7f6ec;
  --bad: #dc2626;
  --bad-soft: #fdecec;
  --pink: #d4537e;
  --track: #e7eaef;
  --radius: 14px;
  --radius-sm: 9px;
  --shadow: 0 1px 2px rgba(16,24,40,.06), 0 10px 28px rgba(16,24,40,.07);
  --maxw: 1060px;
  --readw: 760px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
}

[data-theme="dark"] {
  --bg: #0e1117;
  --card: #161b22;
  --page: #0b0e13;
  --text: #e6e9ee;
  --muted: #98a2b3;
  --faint: #6b7480;
  --border: #272d38;
  --accent: #818cf8;
  --accent-soft: #1d2030;
  --accent-text: #c7ccfb;
  --teal: #2dd4bf;
  --teal-soft: #14282a;
  --teal-text: #6ee7d7;
  --amber-soft: #2a2113;
  --amber-text: #f0c27b;
  --good: #4ade80;
  --good-soft: #14271a;
  --bad: #f87171;
  --bad-soft: #2a1718;
  --pink: #f472a6;
  --track: #2a313c;
  --shadow: 0 1px 2px rgba(0,0,0,.4), 0 10px 28px rgba(0,0,0,.35);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme]) {
    --bg: #0e1117; --card: #161b22; --page: #0b0e13; --text: #e6e9ee;
    --muted: #98a2b3; --faint: #6b7480; --border: #272d38; --accent: #818cf8;
    --accent-soft: #1d2030; --accent-text: #c7ccfb; --teal: #2dd4bf;
    --teal-soft: #14282a; --teal-text: #6ee7d7; --amber-soft: #2a2113;
    --amber-text: #f0c27b; --good: #4ade80; --good-soft: #14271a; --bad: #f87171;
    --bad-soft: #2a1718; --pink: #f472a6; --track: #2a313c;
  }
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}
.container { width: 100%; max-width: var(--maxw); margin: 0 auto; padding: 0 20px; }

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

h1,h2,h3 { line-height: 1.25; font-weight: 700; }
h1 { font-size: clamp(1.7rem, 4vw, 2.5rem); margin: 0 0 .4em; }
h2 { font-size: 1.45rem; margin: 1.6em 0 .5em; }
h3 { font-size: 1.12rem; margin: 1.3em 0 .4em; }
p { margin: 0 0 1em; }

code, .mono {
  font-family: var(--mono);
  background: var(--accent-soft); color: var(--accent-text);
  padding: .12em .4em; border-radius: 6px; font-size: .92em;
}

:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; border-radius: 4px; }

/* ---------- Header / nav ---------- */
.site-header {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in srgb, var(--card) 90%, transparent);
  backdrop-filter: saturate(140%) blur(8px);
  border-bottom: 1px solid var(--border);
}
.nav-inner { display: flex; align-items: center; gap: 12px; height: 60px; }
.brand { display: inline-flex; align-items: center; gap: 9px; font-weight: 800; font-size: 1.12rem; color: var(--text); }
.brand:hover { text-decoration: none; }
.brand .logo { width: 26px; height: 26px; flex: 0 0 auto; }
.nav-spacer { flex: 1; }
.main-nav { display: flex; gap: 4px; align-items: center; }
.main-nav a { color: var(--muted); font-weight: 600; font-size: .93rem; padding: 7px 11px; border-radius: 8px; }
.main-nav a:hover { color: var(--text); background: var(--accent-soft); text-decoration: none; }
.main-nav a.active { color: var(--accent); }

.icon-btn {
  width: 36px; height: 36px; border-radius: 9px; border: 1px solid var(--border);
  background: var(--card); color: var(--text); cursor: pointer;
  display: inline-flex; align-items: center; justify-content: center; font-size: 1.05rem;
}
.icon-btn:hover { border-color: var(--accent); }

.hdr-progress { display: inline-flex; align-items: center; gap: 8px; font-size: .82rem; color: var(--muted); }
.hdr-progress .bar { width: 70px; height: 6px; border-radius: 99px; background: var(--track); overflow: hidden; }
.hdr-progress .bar > i { display: block; height: 100%; background: var(--accent); border-radius: 99px; }
.review-nudge { font-size: .8rem; color: var(--teal-text); font-weight: 600; }

.nav-toggle { display: none; }

/* Account */
.acct { position: relative; }
.acct-menu {
  position: absolute; right: 0; top: 44px; min-width: 200px;
  background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-sm);
  box-shadow: var(--shadow); padding: 8px; display: none;
}
.acct-menu.open { display: block; }
.acct-menu button, .acct-menu a {
  display: flex; align-items: center; gap: 9px; width: 100%; text-align: left;
  font: inherit; font-size: .9rem; padding: 9px 10px; border: 0; background: none;
  color: var(--text); border-radius: 7px; cursor: pointer;
}
.acct-menu button:hover, .acct-menu a:hover { background: var(--accent-soft); text-decoration: none; }
.acct-menu .sep { height: 1px; background: var(--border); margin: 6px 2px; }
.avatar { width: 30px; height: 30px; border-radius: 50%; background: var(--accent); color: #fff;
  display: inline-flex; align-items: center; justify-content: center; font-size: .8rem; font-weight: 700; }

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex; align-items: center; gap: 8px; font-family: inherit;
  font-weight: 600; font-size: .95rem; padding: 11px 20px; border-radius: 10px;
  border: 1px solid var(--border); background: var(--card); color: var(--text);
  cursor: pointer; transition: transform .06s ease, border-color .15s ease, background .15s ease;
}
.btn:hover { text-decoration: none; border-color: var(--accent); }
.btn:active { transform: scale(.98); }
.btn-primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn-primary:hover { background: color-mix(in srgb, var(--accent) 86%, #000); border-color: transparent; }
.btn-sm { padding: 8px 14px; font-size: .88rem; }

/* ---------- Hero ---------- */
.hero { padding: 60px 0 36px; text-align: center; }
.hero p.lead { font-size: 1.18rem; color: var(--muted); max-width: 600px; margin: 0 auto 1.7em; }
.hero-actions { display: flex; gap: 12px; justify-content: center; flex-wrap: wrap; }

/* ---------- Cards / grid ---------- */
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 18px; }
.card {
  display: flex; flex-direction: column; background: var(--card);
  border: 1px solid var(--border); border-radius: var(--radius); padding: 20px;
  box-shadow: var(--shadow); transition: transform .12s ease, border-color .12s ease; position: relative;
}
a.card:hover { text-decoration: none; transform: translateY(-3px); border-color: var(--accent); }
.card h3 { margin: 0 0 .35em; color: var(--text); }
.card p { color: var(--muted); margin: 0 0 1em; font-size: .94rem; flex: 1; }
.card .start { font-weight: 700; color: var(--accent); }
.card.is-next { border-color: var(--accent); border-width: 2px; }

.badge {
  align-self: flex-start; font-size: .7rem; font-weight: 700; letter-spacing: .03em;
  text-transform: uppercase; padding: 4px 10px; border-radius: 999px;
  background: var(--teal-soft); color: var(--teal-text); margin-bottom: 11px;
}
.badge.next { background: var(--accent-soft); color: var(--accent-text); }
.check { position: absolute; top: 16px; right: 16px; color: var(--good); font-size: 1.25rem; }

.lesson-num { font-size: .78rem; color: var(--faint); font-weight: 700; }

/* ---------- Lesson layout / learning arc ---------- */
.lesson { padding: 32px 0 30px; max-width: var(--readw); }
.eyebrow { font-size: .78rem; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: var(--teal); margin-bottom: 6px; }
.intro { font-size: 1.08rem; color: var(--muted); }
.arc-step { margin: 30px 0; }
.arc-step > h2 { display: flex; align-items: center; gap: 9px; }
.arc-step > h2 .ti { color: var(--accent); font-size: 1.2em; }

.viz-panel { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 20px; box-shadow: var(--shadow); margin: 16px 0; }
canvas.viz { width: 100%; display: block; }
.linked-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 12px; }
.mini { background: var(--bg); border: 1px solid var(--border); border-radius: var(--radius-sm); padding: 13px; }
.mini .lbl { font-size: .68rem; font-weight: 700; text-transform: uppercase; letter-spacing: .04em; color: var(--muted); margin-bottom: 8px; }

.controls { display: grid; gap: 14px; margin-top: 16px; }
.control { display: flex; align-items: center; gap: 14px; flex-wrap: wrap; }
.control label { font-weight: 600; min-width: 110px; color: var(--text); }
.control input[type="range"] { flex: 1; min-width: 150px; accent-color: var(--accent); height: 26px; }
.control .val { font-weight: 700; min-width: 56px; text-align: right; font-variant-numeric: tabular-nums; color: var(--accent); }
.control input[type="number"], .control select {
  font-family: inherit; font-size: 1rem; padding: 9px 11px; border-radius: 8px;
  border: 1px solid var(--border); background: var(--bg); color: var(--text);
}
.seg { display: inline-flex; border: 1px solid var(--border); border-radius: var(--radius-sm); overflow: hidden; }
.seg button { font-family: inherit; font-size: .92rem; font-weight: 600; padding: 8px 14px; border: 0; background: var(--card); color: var(--muted); cursor: pointer; }
.seg button.active { background: var(--accent); color: #fff; }

.readout { display: flex; flex-wrap: wrap; gap: 10px 26px; margin-top: 16px; padding-top: 15px; border-top: 1px solid var(--border); font-size: 1.05rem; }
.readout b { font-variant-numeric: tabular-nums; }
.result-big { font-size: 1.55rem; font-weight: 800; color: var(--accent); font-variant-numeric: tabular-nums; }

/* Callouts */
.callout { border-left: 4px solid var(--teal); border-radius: 0 10px 10px 0; padding: 13px 17px; margin: 16px 0; background: var(--teal-soft); }
.callout .h { font-weight: 700; font-size: .85rem; margin-bottom: 3px; display: flex; align-items: center; gap: 7px; }
.callout p:last-child { margin-bottom: 0; }
.callout.example { background: var(--teal-soft); border-color: var(--teal); }
.callout.example .h { color: var(--teal-text); }
.callout.mistake { background: var(--amber-soft); border-color: #d9920a; }
.callout.mistake .h, .callout.mistake p { color: var(--amber-text); }

/* Predict */
.predict { background: var(--accent-soft); border: 1px solid var(--border); border-radius: var(--radius-sm); padding: 16px; }
.predict .opts { display: flex; gap: 10px; flex-wrap: wrap; margin: 10px 0; }
.predict .opts button { flex: 1; min-width: 120px; }
.predict .verdict { font-weight: 600; margin-top: 8px; }

/* Recap */
.recap { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 18px 22px; }
.recap ul { margin: 0 0 .5em; padding-left: 1.2em; }
.recap li { margin: .3em 0; }

/* ---------- Quiz ---------- */
.quiz { display: grid; gap: 16px; }
.q { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 18px; }
.q .stem { font-weight: 600; margin-bottom: 12px; }
.q .choices { display: grid; gap: 8px; }
.q .choice {
  display: block; width: 100%; text-align: left; font: inherit; padding: 11px 14px;
  border: 1px solid var(--border); border-radius: var(--radius-sm); background: var(--bg);
  color: var(--text); cursor: pointer;
}
.q .choice:hover { border-color: var(--accent); }
.q .choice.correct { border-color: var(--good); background: var(--good-soft); }
.q .choice.wrong { border-color: var(--bad); background: var(--bad-soft); }
.q .choice:disabled { cursor: default; }
.q .numrow { display: flex; gap: 8px; flex-wrap: wrap; }
.q .numrow input { font: inherit; font-size: 1rem; padding: 10px 12px; border-radius: 8px; border: 1px solid var(--border); background: var(--bg); color: var(--text); width: 140px; }
.q .fb { margin-top: 11px; font-size: .94rem; display: none; }
.q .fb.show { display: block; }
.q .fb.ok { color: var(--good); }
.q .fb.no { color: var(--bad); }
.q .tools { margin-top: 10px; display: flex; gap: 14px; }
.q .tools button { background: none; border: 0; color: var(--accent); font: inherit; font-weight: 600; cursor: pointer; padding: 0; }
.q .hint, .q .solution { margin-top: 10px; font-size: .92rem; color: var(--muted); display: none; }
.q .hint.show, .q .solution.show { display: block; }
.quiz-score { font-weight: 700; font-size: 1.05rem; }
.quiz-done { background: var(--good-soft); border: 1px solid var(--good); color: var(--good); border-radius: var(--radius); padding: 14px 18px; font-weight: 600; display: none; }
.quiz-done.show { display: block; }

/* ---------- Glossary ---------- */
.glossary dl { display: grid; gap: 14px; }
.glossary dt { font-weight: 700; font-size: 1.05rem; }
.glossary dd { margin: 4px 0 0; color: var(--muted); }
.glossary .term { scroll-margin-top: 80px; background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-sm); padding: 14px 18px; }
.glossary .term:target { border-color: var(--accent); }

/* ---------- Badges grid ---------- */
.badges { display: flex; flex-wrap: wrap; gap: 12px; }
.bdg { display: flex; align-items: center; gap: 10px; padding: 10px 14px; border-radius: 99px; border: 1px solid var(--border); background: var(--card); font-size: .88rem; font-weight: 600; }
.bdg.locked { opacity: .45; }
.bdg .ti { font-size: 1.2rem; color: var(--accent); }

/* ---------- Prev/next ---------- */
.lesson-nav { display: flex; justify-content: space-between; gap: 12px; margin-top: 36px; padding-top: 20px; border-top: 1px solid var(--border); }
.lesson-nav a { font-weight: 600; }
.lesson-nav .spacer { flex: 1; }

/* ---------- Consent banner ---------- */
.consent {
  position: fixed; left: 16px; right: 16px; bottom: 16px; z-index: 100; max-width: 560px;
  margin: 0 auto; background: var(--card); border: 1px solid var(--border);
  border-radius: var(--radius); box-shadow: var(--shadow); padding: 16px 18px;
  display: none; align-items: center; gap: 14px; flex-wrap: wrap;
}
.consent.show { display: flex; }
.consent p { margin: 0; flex: 1; min-width: 220px; font-size: .9rem; color: var(--muted); }
.consent .actions { display: flex; gap: 8px; }

/* ---------- Footer ---------- */
.site-footer { border-top: 1px solid var(--border); margin-top: 56px; padding: 26px 0; color: var(--muted); font-size: .9rem; }
.site-footer .fwrap { display: flex; gap: 16px; flex-wrap: wrap; justify-content: space-between; align-items: center; }
.site-footer a { color: var(--muted); }
.site-footer a:hover { color: var(--text); }

/* ---------- Utilities ---------- */
.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; }
.center { text-align: center; }
.muted { color: var(--muted); }
.stack { display: grid; gap: 10px; }

/* ---------- Responsive ---------- */
@media (max-width: 640px) {
  .nav-toggle { display: inline-flex; }
  .main-nav {
    position: absolute; top: 60px; right: 12px; flex-direction: column; align-items: stretch;
    background: var(--card); border: 1px solid var(--border); border-radius: var(--radius-sm);
    box-shadow: var(--shadow); padding: 8px; min-width: 180px; display: none;
  }
  .main-nav.open { display: flex; }
  .hdr-progress .bar { display: none; }
  .hero { padding: 40px 0 28px; }
}

/* ---------- Print (cheat-sheet) ---------- */
@media print {
  .site-header, .site-footer, .controls, .viz-panel, .quiz, .predict,
  .lesson-nav, .consent, .no-print { display: none !important; }
  body { background: #fff; color: #000; }
  .lesson { max-width: 100%; padding: 0; }
  .callout, .recap { border: 1px solid #999; background: #fff; }
  a { color: #000; text-decoration: none; }
}

/* Respect reduced motion */
@media (prefers-reduced-motion: reduce) {
  * { animation-duration: .001ms !important; transition-duration: .001ms !important; scroll-behavior: auto !important; }
}