body{margin:0}[hidden]{display:none!important}img{max-width:100%}


/* Layout: collapsible chapter sidebar + top bar + reading column (max 820px) with sticky lesson-flow rail on wide screens.
   Palette: sunset orange → coral → violet over violet-tinted neutrals. */
:root {
  --bg: #fbf8fd;
  --surface: #ffffff;
  --surface-2: #f4eff9;
  --ink: #23182f;
  --ink-2: #5a4c6b;
  --ink-3: #8a7c99;
  --line: #e6ddef;
  --orange: #f0682e;
  --coral: #f2545b;
  --violet: #7646d8;
  --violet-ink: #5a2fc0;
  --teal: #12897c;
  --good: #188a55;
  --good-bg: #e5f6ec;
  --bad: #c43a3a;
  --bad-bg: #fde9e8;
  --warn-bg: #fff3e4;
  --chart-grid: #ece4f3;
  --chart-axis: #7f7190;
  --c1: #7646d8;
  --c2: #f0682e;
  --c3: #12897c;
  --c4: #e0457b;
  --shadow: 0 1px 2px rgba(45, 20, 70, .06), 0 6px 24px rgba(45, 20, 70, .07);
  --grad: linear-gradient(115deg, #f7943a 0%, #f2545b 45%, #7646d8 100%);
  --grad-soft: linear-gradient(115deg, rgba(247,148,58,.14), rgba(242,84,91,.12) 45%, rgba(118,70,216,.14));
  --font-display: "Bricolage Grotesque", "Avenir Next", "Segoe UI", system-ui, sans-serif;
  --font-body: "Atkinson Hyperlegible", "Segoe UI", system-ui, -apple-system, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --sidebar-w: 292px;
  --radius: 14px;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #130e1b; --surface: #1c1527; --surface-2: #251c33; --ink: #f3edf9; --ink-2: #c6b9d6; --ink-3: #9384a6;
    --line: #34294a; --orange: #ff8a4c; --coral: #ff6f75; --violet: #a483ff; --violet-ink: #b99cff; --teal: #3cc7b4;
    --good: #4fd08d; --good-bg: #173527; --bad: #ff7a72; --bad-bg: #3a1a1d; --warn-bg: #3a2a14;
    --chart-grid: #2c2240; --chart-axis: #a596b8; --c1: #a483ff; --c2: #ff8a4c; --c3: #3cc7b4; --c4: #ff6f9e;
    --shadow: 0 1px 2px rgba(0,0,0,.3), 0 8px 28px rgba(0,0,0,.35);
    --grad-soft: linear-gradient(115deg, rgba(255,138,76,.16), rgba(255,111,117,.12) 45%, rgba(164,131,255,.18));
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #130e1b; --surface: #1c1527; --surface-2: #251c33; --ink: #f3edf9; --ink-2: #c6b9d6; --ink-3: #9384a6;
  --line: #34294a; --orange: #ff8a4c; --coral: #ff6f75; --violet: #a483ff; --violet-ink: #b99cff; --teal: #3cc7b4;
  --good: #4fd08d; --good-bg: #173527; --bad: #ff7a72; --bad-bg: #3a1a1d; --warn-bg: #3a2a14;
  --chart-grid: #2c2240; --chart-axis: #a596b8; --c1: #a483ff; --c2: #ff8a4c; --c3: #3cc7b4; --c4: #ff6f9e;
  --shadow: 0 1px 2px rgba(0,0,0,.3), 0 8px 28px rgba(0,0,0,.35);
  --grad-soft: linear-gradient(115deg, rgba(255,138,76,.16), rgba(255,111,117,.12) 45%, rgba(164,131,255,.18));
  color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body { background: var(--bg); color: var(--ink); font-family: var(--font-body); font-size: 16px; line-height: 1.62; -webkit-font-smoothing: antialiased; }
body::before { content: ""; position: fixed; inset: 0 0 auto; height: env(safe-area-inset-top, 0px); z-index: 60; background: var(--surface); }
a { color: var(--violet-ink); }
h1, h2, h3, h4 { font-family: var(--font-display); line-height: 1.18; text-wrap: balance; margin: 0; letter-spacing: -0.01em; }
h1 { font-size: clamp(1.9rem, 1.3rem + 2.2vw, 2.7rem); font-weight: 700; }
h2 { font-size: 1.55rem; font-weight: 650; }
h3 { font-size: 1.18rem; font-weight: 650; }
h4 { font-size: 1rem; font-weight: 650; }
p { margin: 0; }
code, pre, kbd { font-family: var(--font-mono); }
:focus-visible { outline: 3px solid var(--violet); outline-offset: 2px; border-radius: 6px; }
button { font: inherit; color: inherit; }
.sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }

/* ---------- Shell ---------- */
.app { display: grid; grid-template-columns: var(--sidebar-w) minmax(0, 1fr); min-height: 100%; }
.app.collapsed { grid-template-columns: 0 minmax(0, 1fr); }
.sidebar { position: sticky; top: 0; height: 100vh; overflow-y: auto; background: var(--surface); border-right: 1px solid var(--line); padding: calc(env(safe-area-inset-top, 0px) + 18px) 14px 24px max(14px, env(safe-area-inset-left, 0px)); display: flex; flex-direction: column; gap: 14px; transition: transform .25s ease; z-index: 40; }
.app.collapsed .sidebar { transform: translateX(-100%); visibility: hidden; }
.brand { display: flex; align-items: center; gap: 10px; padding: 4px 6px 8px; text-decoration: none; color: var(--ink); }
.brand-mark { width: 38px; height: 38px; border-radius: 11px; background: var(--grad); display: grid; place-items: center; flex: none; }
.brand-mark svg { width: 24px; height: 24px; }
.brand b { font-family: var(--font-display); font-size: 1.05rem; display: block; line-height: 1.1; }
.brand small { color: var(--ink-3); font-size: .76rem; letter-spacing: .04em; text-transform: uppercase; }
.nav-group { display: flex; flex-direction: column; gap: 2px; }
.nav-label { font-size: .72rem; text-transform: uppercase; letter-spacing: .09em; color: var(--ink-3); padding: 8px 8px 4px; font-weight: 700; }
.nav-link { display: flex; align-items: center; gap: 10px; padding: 8px 10px; border-radius: 10px; color: var(--ink-2); text-decoration: none; font-size: .93rem; line-height: 1.3; border: 0; background: none; text-align: left; cursor: pointer; width: 100%; }
.nav-link:hover { background: var(--surface-2); color: var(--ink); }
.nav-link.active { background: var(--grad-soft); color: var(--ink); font-weight: 700; }
.nav-link .num { font-family: var(--font-mono); font-size: .74rem; color: var(--ink-3); min-width: 2.4em; }
.nav-link .tick { margin-left: auto; width: 16px; height: 16px; border-radius: 50%; border: 2px solid var(--line); flex: none; }
.nav-link .tick.done { background: var(--good); border-color: var(--good); box-shadow: inset 0 0 0 2px var(--surface); }
.chap-btn { font-weight: 700; color: var(--ink); }
.chap-btn .ring { width: 22px; height: 22px; flex: none; }
.chap-sections { display: flex; flex-direction: column; gap: 1px; padding-left: 12px; margin-left: 10px; border-left: 2px solid var(--line); }
.chap-sections[hidden] { display: none !important; }

.main { min-width: 0; display: flex; flex-direction: column; }
.topbar { position: sticky; top: env(safe-area-inset-top, 0px); z-index: 30; background: color-mix(in srgb, var(--surface) 88%, transparent); backdrop-filter: blur(10px); border-bottom: 1px solid var(--line); display: flex; align-items: center; gap: 10px; padding-block: 10px; padding-left: max(16px, env(safe-area-inset-left, 0px)); padding-right: max(16px, env(safe-area-inset-right, 0px)); flex-wrap: wrap; }
.icon-btn { width: 40px; height: 40px; border-radius: 10px; border: 1px solid var(--line); background: var(--surface); display: grid; place-items: center; cursor: pointer; flex: none; }
.icon-btn:hover { background: var(--surface-2); }
.icon-btn svg { width: 20px; height: 20px; stroke: currentColor; fill: none; stroke-width: 2; stroke-linecap: round; stroke-linejoin: round; }
.modes { display: flex; gap: 4px; background: var(--surface-2); padding: 4px; border-radius: 12px; }
.modes a { text-decoration: none; color: var(--ink-2); padding: 6px 12px; border-radius: 9px; font-size: .9rem; font-weight: 700; }
.modes a.active { background: var(--surface); color: var(--ink); box-shadow: var(--shadow); }
.spacer { flex: 1; }
.seg { display: inline-flex; border: 1px solid var(--line); border-radius: 10px; overflow: hidden; }
.seg button { border: 0; background: var(--surface); padding: 7px 11px; font-size: .84rem; cursor: pointer; color: var(--ink-2); font-weight: 700; }
.seg button[aria-pressed="true"] { background: var(--ink); color: var(--surface); }
.progressbar { position: absolute; left: 0; bottom: -1px; height: 3px; background: var(--grad); width: 0; transition: width .1s linear; }

.content { padding-block: 28px 80px; padding-left: max(16px, env(safe-area-inset-left, 0px)); padding-right: max(16px, env(safe-area-inset-right, 0px)); display: grid; grid-template-columns: minmax(0, 820px) 220px; gap: 40px; justify-content: center; }
.content.wide { grid-template-columns: minmax(0, 1080px); }
.col { min-width: 0; display: flex; flex-direction: column; gap: 28px; }
.rail { position: sticky; top: 92px; align-self: start; display: flex; flex-direction: column; gap: 2px; font-size: .86rem; }
.rail a { color: var(--ink-3); text-decoration: none; padding: 5px 10px; border-left: 2px solid var(--line); display: flex; gap: 8px; }
.rail a span { font-family: var(--font-mono); font-size: .74rem; }
.rail a.on { color: var(--ink); border-left-color: var(--coral); font-weight: 700; }
@media (max-width: 1180px) { .content { grid-template-columns: minmax(0, 820px); } .rail { display: none; } }
@media (max-width: 860px) {
  .app, .app.collapsed { grid-template-columns: minmax(0, 1fr); }
  .sidebar { position: fixed; inset: 0 auto 0 0; width: min(88vw, 320px); box-shadow: var(--shadow); transform: translateX(-100%); visibility: hidden; }
  .app.drawer-open .sidebar { transform: none; visibility: visible; }
  .scrim { position: fixed; inset: 0; background: rgba(20, 10, 30, .4); z-index: 35; }
  .modes a { padding: 6px 9px; }
}

/* ---------- Generic blocks ---------- */
.hero { border-radius: 22px; padding: clamp(22px, 4vw, 40px); background: var(--grad); color: #fff; position: relative; overflow: hidden; display: grid; gap: 14px; }
.hero h1 { color: #fff; }
.hero p { color: rgba(255,255,255,.92); max-width: 62ch; font-size: 1.05rem; }
.hero canvas { position: absolute; inset: 0; width: 100%; height: 100%; opacity: .35; pointer-events: none; }
.hero > *:not(canvas) { position: relative; }
.hero .eyebrow { color: rgba(255,255,255,.85); }
.eyebrow { font-size: .76rem; letter-spacing: .1em; text-transform: uppercase; font-weight: 700; color: var(--coral); }
.btn { display: inline-flex; align-items: center; gap: 8px; border: 1px solid var(--line); background: var(--surface); color: var(--ink); padding: 9px 16px; border-radius: 11px; font-weight: 700; font-size: .92rem; cursor: pointer; text-decoration: none; transition: transform .15s ease, box-shadow .15s ease; }
.btn:hover { transform: translateY(-1px); box-shadow: var(--shadow); }
.btn.primary { background: var(--ink); color: var(--surface); border-color: var(--ink); }
.btn.light { background: #fff; color: #2a1640; border-color: #fff; }
.btn.small { padding: 6px 11px; font-size: .84rem; border-radius: 9px; }
.btn:disabled { opacity: .45; cursor: not-allowed; transform: none; box-shadow: none; }
.row { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; }
.grid { display: grid; gap: 16px; }
.g2 { grid-template-columns: repeat(auto-fit, minmax(min(100%, 300px), 1fr)); }
.g3 { grid-template-columns: repeat(auto-fit, minmax(min(100%, 230px), 1fr)); }
.card { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 18px 20px; min-width: 0; }
.muted { color: var(--ink-2); }
.small { font-size: .88rem; }
.tag { display: inline-flex; align-items: center; gap: 6px; font-size: .74rem; font-weight: 700; padding: 3px 9px; border-radius: 999px; background: var(--surface-2); color: var(--ink-2); letter-spacing: .02em; }
.tag.src { background: color-mix(in srgb, var(--violet) 13%, transparent); color: var(--violet-ink); }
.tag.added { background: color-mix(in srgb, var(--orange) 15%, transparent); color: color-mix(in srgb, var(--orange) 75%, var(--ink)); }
.tag.lv1 { color: var(--good); } .tag.lv2 { color: color-mix(in srgb, var(--orange) 80%, var(--ink)); } .tag.lv3 { color: var(--coral); }
.dots { display: inline-flex; gap: 3px; } .dots i { width: 7px; height: 7px; border-radius: 50%; background: var(--line); } .dots i.on { background: var(--coral); }

/* ---------- Dashboard ---------- */
.stats { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 170px), 1fr)); gap: 12px; }
.stat { background: rgba(255,255,255,.16); border: 1px solid rgba(255,255,255,.3); border-radius: 14px; padding: 12px 14px; }
.stat b { display: block; font-family: var(--font-display); font-size: 1.6rem; line-height: 1.1; font-variant-numeric: tabular-nums; }
.stat span { font-size: .82rem; opacity: .9; }
.chap-card { display: flex; flex-direction: column; gap: 12px; }
.chap-card header { display: flex; gap: 14px; align-items: flex-start; }
.chap-no { font-family: var(--font-display); font-size: 2.4rem; font-weight: 800; line-height: .9; background: var(--grad); -webkit-background-clip: text; background-clip: text; color: transparent; }
.meter { height: 8px; border-radius: 99px; background: var(--surface-2); overflow: hidden; }
.meter > i { display: block; height: 100%; background: var(--grad); border-radius: 99px; }
.sec-list { list-style: none; padding: 0; margin: 0; display: flex; flex-direction: column; gap: 2px; }
.sec-list a { display: flex; gap: 10px; align-items: center; padding: 7px 8px; border-radius: 9px; text-decoration: none; color: var(--ink); font-size: .93rem; }
.sec-list a:hover { background: var(--surface-2); }
.sec-list .num { font-family: var(--font-mono); font-size: .76rem; color: var(--ink-3); min-width: 2.6em; }
.sec-list .meta { margin-left: auto; color: var(--ink-3); font-size: .78rem; white-space: nowrap; }
.objectives { margin: 0; padding-left: 1.2em; display: grid; gap: 4px; }

/* ---------- Lesson ---------- */
.lesson-head { display: grid; gap: 12px; }
.lesson-head .row { gap: 8px; }
.flow { display: flex; gap: 6px; flex-wrap: wrap; }
.flow a { font-size: .8rem; text-decoration: none; padding: 4px 10px; border-radius: 99px; border: 1px solid var(--line); color: var(--ink-2); background: var(--surface); }
.flow a:hover { border-color: var(--coral); color: var(--ink); }
.block { display: grid; gap: 14px; scroll-margin-top: 90px; }
.block > header { display: flex; align-items: center; gap: 12px; }
.block > header .step { width: 34px; height: 34px; border-radius: 10px; display: grid; place-items: center; font-family: var(--font-display); font-weight: 800; color: #fff; background: var(--grad); flex: none; font-size: .95rem; }
.block > header h2 { font-size: 1.32rem; }
.prose { display: grid; gap: 12px; max-width: 72ch; }
.prose ul, .prose ol { margin: 0; padding-left: 1.3em; display: grid; gap: 5px; }
.callout { border-radius: 12px; padding: 14px 16px; background: var(--surface-2); border: 1px solid var(--line); display: grid; gap: 6px; }
.callout.tip { background: color-mix(in srgb, var(--teal) 9%, var(--surface)); border-color: color-mix(in srgb, var(--teal) 30%, var(--line)); }
.callout.warn { background: var(--warn-bg); border-color: color-mix(in srgb, var(--orange) 35%, var(--line)); }
.callout.exam { background: color-mix(in srgb, var(--violet) 9%, var(--surface)); border-color: color-mix(in srgb, var(--violet) 30%, var(--line)); }
.callout > b:first-child { font-family: var(--font-display); font-size: .95rem; }
.beg { border-left: 4px solid var(--orange); background: var(--surface); border-radius: 0 12px 12px 0; padding: 12px 16px; display: grid; gap: 6px; }
.beg::before { content: "In plain English"; font-size: .72rem; text-transform: uppercase; letter-spacing: .1em; font-weight: 700; color: var(--orange); }
body.lv-advanced .beg { display: none; }
details.adv { border: 1px dashed color-mix(in srgb, var(--violet) 45%, var(--line)); border-radius: 12px; padding: 10px 14px; background: var(--surface); }
details.adv > summary { cursor: pointer; font-weight: 700; color: var(--violet-ink); font-size: .93rem; }
details.adv[open] > summary { margin-bottom: 8px; }
details.adv > div { display: grid; gap: 10px; }
.src-note { font-size: .8rem; color: var(--ink-3); display: flex; gap: 6px; flex-wrap: wrap; align-items: center; }

/* Formula card */
.eq { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px 18px; display: grid; gap: 8px; }
.eq .eq-title { font-size: .78rem; text-transform: uppercase; letter-spacing: .08em; color: var(--ink-3); font-weight: 700; }
.eq .math { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }
.eq .why { font-size: .92rem; color: var(--ink-2); }
.eq button.explain { justify-self: start; }
.sym { width: 100%; border-collapse: collapse; font-size: .92rem; }
.sym td { padding: 6px 8px; border-top: 1px solid var(--line); vertical-align: top; }
.sym td:first-child { width: 120px; white-space: nowrap; }

/* Derivation stepper */
.deriv { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; }
.deriv header { display: flex; justify-content: space-between; align-items: center; gap: 10px; padding: 12px 16px; background: var(--surface-2); flex-wrap: wrap; }
.deriv ol { list-style: none; margin: 0; padding: 8px 16px 14px; counter-reset: d; display: grid; gap: 2px; }
.deriv li { counter-increment: d; display: grid; grid-template-columns: 28px minmax(0,1fr); gap: 4px 10px; padding: 8px 0; border-bottom: 1px dashed var(--line); animation: rise .35s ease both; }
.deriv li:last-child { border-bottom: 0; }
.deriv li::before { content: counter(d); font-family: var(--font-mono); font-size: .76rem; color: var(--ink-3); padding-top: 6px; }
.deriv li .m { overflow-x: auto; min-width: 0; }
.deriv li .j { grid-column: 2; font-size: .86rem; color: var(--ink-2); }
.deriv li[hidden] { display: none !important; }
@keyframes rise { from { opacity: .2; transform: translateY(6px); } to { opacity: 1; transform: none; } }

/* Widgets */
.widget { background: var(--surface); border: 1px solid var(--line); border-radius: 18px; padding: 18px; display: grid; gap: 14px; box-shadow: var(--shadow); min-width: 0; }
.widget > .w-head { display: flex; justify-content: space-between; gap: 10px; align-items: baseline; flex-wrap: wrap; }
.widget > .w-head h3 { font-size: 1.05rem; }
.controls { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 190px), 1fr)); gap: 12px 18px; }
.ctrl { display: grid; gap: 4px; font-size: .86rem; min-width: 0; }
.ctrl label { display: flex; justify-content: space-between; gap: 8px; color: var(--ink-2); font-weight: 700; }
.ctrl output { font-family: var(--font-mono); color: var(--ink); font-weight: 400; font-variant-numeric: tabular-nums; }
.ctrl select, .ctrl input[type=number], .ctrl input[type=text] { font: inherit; padding: 7px 10px; border-radius: 9px; border: 1px solid var(--line); background: var(--surface); color: var(--ink); width: 100%; }
input[type=range] { width: 100%; accent-color: var(--coral); height: 24px; }
.chart { width: 100%; overflow-x: auto; }
.chart svg { display: block; width: 100%; height: auto; }
.chart svg text { fill: var(--chart-axis); font-family: var(--font-body); }
.chart .grid line { stroke: var(--chart-grid); }
.chart .axis line, .chart .axis path { stroke: var(--chart-axis); }
.legend { display: flex; gap: 14px; flex-wrap: wrap; font-size: .82rem; color: var(--ink-2); }
.legend i { display: inline-block; width: 14px; height: 3px; border-radius: 2px; vertical-align: middle; margin-right: 6px; }
.readout { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 140px), 1fr)); gap: 10px; }
.readout div { background: var(--surface-2); border-radius: 11px; padding: 9px 12px; }
.readout span { display: block; font-size: .74rem; color: var(--ink-3); text-transform: uppercase; letter-spacing: .06em; font-weight: 700; }
.readout b { font-family: var(--font-mono); font-size: 1.02rem; font-variant-numeric: tabular-nums; font-weight: 600; }
.tbl-wrap { overflow-x: auto; border: 1px solid var(--line); border-radius: 12px; }
table.t { border-collapse: collapse; width: 100%; font-size: .9rem; font-variant-numeric: tabular-nums; }
table.t th, table.t td { padding: 7px 12px; text-align: right; border-bottom: 1px solid var(--line); white-space: nowrap; }
table.t th:first-child, table.t td:first-child { text-align: left; }
table.t thead th { background: var(--surface-2); font-size: .78rem; text-transform: uppercase; letter-spacing: .05em; color: var(--ink-2); }
table.t tr:last-child td { border-bottom: 0; }
table.t td.best { color: var(--good); font-weight: 700; }
.pill { display: inline-block; padding: 2px 10px; border-radius: 99px; font-size: .8rem; font-weight: 700; }
.pill.ok { background: var(--good-bg); color: var(--good); }
.pill.no { background: var(--bad-bg); color: var(--bad); }

/* Code */
.code { border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; background: var(--surface); min-width: 0; }
.code-tabs { display: flex; align-items: center; gap: 4px; padding: 8px 10px; background: var(--surface-2); border-bottom: 1px solid var(--line); flex-wrap: wrap; }
.code-tabs button.tab { border: 0; background: none; padding: 6px 12px; border-radius: 8px; cursor: pointer; font-weight: 700; font-size: .84rem; color: var(--ink-2); }
.code-tabs button.tab[aria-selected="true"] { background: var(--surface); color: var(--ink); box-shadow: var(--shadow); }
.code-tabs .copy { margin-left: auto; }
.code pre { margin: 0; padding: 16px 18px; overflow-x: auto; font-size: .84rem; line-height: 1.6; background: var(--surface); color: var(--ink); tab-size: 2; }
.code .out { border-top: 1px solid var(--line); padding: 12px 18px; display: grid; gap: 6px; background: color-mix(in srgb, var(--surface-2) 60%, var(--surface)); }
.code .out pre { padding: 0; background: none; font-size: .8rem; color: var(--ink-2); }
.code .out .lbl { font-size: .74rem; text-transform: uppercase; letter-spacing: .07em; color: var(--ink-3); font-weight: 700; }
.code .notes { padding: 12px 18px 14px; border-top: 1px solid var(--line); font-size: .9rem; display: grid; gap: 6px; }
.code .notes ol { margin: 0; padding-left: 1.3em; display: grid; gap: 4px; }
.token.comment { color: var(--ink-3); font-style: italic; }
.token.string { color: var(--teal); }
.token.keyword, .token.boolean { color: var(--violet-ink); font-weight: 600; }
.token.function { color: var(--coral); }
.token.number { color: color-mix(in srgb, var(--orange) 85%, var(--ink)); }
.token.operator, .token.punctuation { color: var(--ink-2); }
:not(pre) > code { background: var(--surface-2); padding: 1px 6px; border-radius: 6px; font-size: .88em; }

/* Quiz */
.q { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 16px 18px; display: grid; gap: 12px; }
.q .q-meta { display: flex; gap: 8px; flex-wrap: wrap; align-items: center; }
.q .q-text { font-weight: 700; display: grid; gap: 8px; }
.opts { display: grid; gap: 8px; }
.opt { display: flex; gap: 10px; align-items: flex-start; padding: 10px 12px; border-radius: 11px; border: 1.5px solid var(--line); background: var(--surface); cursor: pointer; text-align: left; width: 100%; }
.opt:hover { border-color: var(--violet); }
.opt .key { font-family: var(--font-mono); font-size: .8rem; width: 24px; height: 24px; border-radius: 7px; background: var(--surface-2); display: grid; place-items: center; flex: none; }
.opt.sel { border-color: var(--violet); background: color-mix(in srgb, var(--violet) 7%, var(--surface)); }
.opt.right { border-color: var(--good); background: var(--good-bg); }
.opt.wrong { border-color: var(--bad); background: var(--bad-bg); }
.feedback { border-radius: 11px; padding: 12px 14px; display: grid; gap: 8px; }
.feedback.ok { background: var(--good-bg); }
.feedback.no { background: var(--bad-bg); }
.feedback b { font-family: var(--font-display); }
.num-in { display: flex; gap: 8px; flex-wrap: wrap; }
.num-in input { font: inherit; padding: 8px 12px; border-radius: 10px; border: 1.5px solid var(--line); background: var(--surface); color: var(--ink); width: 160px; font-family: var(--font-mono); }
.scorebar { display: flex; gap: 14px; align-items: center; flex-wrap: wrap; }

/* Flashcards */
.flash { perspective: 1200px; cursor: pointer; }
.flash-inner { position: relative; min-height: 240px; transition: transform .5s ease; transform-style: preserve-3d; }
.flash.flipped .flash-inner { transform: rotateY(180deg); }
.flash-face { position: absolute; inset: 0; backface-visibility: hidden; border-radius: 20px; padding: 26px; display: grid; align-content: center; gap: 10px; border: 1px solid var(--line); background: var(--surface); box-shadow: var(--shadow); overflow: auto; }
.flash-face.front { background: var(--grad); color: #fff; border: 0; }
.flash-face.front h3 { font-size: 1.5rem; color: #fff; }
.flash-face.back { transform: rotateY(180deg); }

/* Model-building cycle */
.cycle { display: grid; grid-template-columns: repeat(auto-fit, minmax(min(100%, 200px), 1fr)); gap: 12px; }
.cycle button { text-align: left; border: 1.5px solid var(--line); background: var(--surface); border-radius: 14px; padding: 14px; cursor: pointer; display: grid; gap: 4px; }
.cycle button[aria-pressed="true"] { border-color: var(--coral); background: var(--grad-soft); }
.cycle button b { font-family: var(--font-display); }

.prevnext { display: flex; justify-content: space-between; gap: 12px; flex-wrap: wrap; padding-top: 10px; border-top: 1px solid var(--line); }
.prevnext a { flex: 1 1 240px; text-decoration: none; color: var(--ink); border: 1px solid var(--line); border-radius: 14px; padding: 12px 16px; background: var(--surface); display: grid; gap: 2px; }
.prevnext a:hover { border-color: var(--coral); }
.prevnext a small { color: var(--ink-3); }
.prevnext a.next { text-align: right; }
.complete-bar { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; padding: 16px 18px; border-radius: 16px; background: var(--grad-soft); border: 1px solid var(--line); }

.fade-in { animation: rise .4s ease both; }
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation: none !important; transition: none !important; scroll-behavior: auto !important; }
}
mjx-container { max-width: 100%; }
mjx-container[display="true"] { overflow-x: auto; overflow-y: hidden; margin: .4em 0 !important; }

/* Keep grid tracks from growing to their widest child (code, long equations) on small screens */
.block, .prose, .widget, .eq, .q, .lesson-head, .callout, .feedback, .card.grid, .grid:not(.g2):not(.g3), details.adv > div { grid-template-columns: minmax(0, 1fr); }
.block-body, .pane, .code, .widget > *, .prose > * { min-width: 0; }
mjx-container:not([display="true"]) { display: inline-block; max-width: 100%; overflow-x: auto; overflow-y: hidden; vertical-align: middle; }

/* ===== TD/TP workbook ===== */
.tp-page { gap: 18px; }
.tp-tabs { align-self: start; flex-wrap: wrap; }
.tp-tabs a small { font-weight: 600; opacity: .7; margin-left: 4px; }
.tp-toolbar { display: grid; gap: 12px; grid-template-columns: minmax(0, 1fr); }
.tp-prog { display: grid; gap: 6px; }
.tp-switch { display: flex; gap: 8px; align-items: center; font-size: .92rem; cursor: pointer; }
.tp-index { display: flex; flex-wrap: wrap; gap: 8px; }
.tp-index a { display: inline-flex; gap: 6px; align-items: baseline; text-decoration: none; padding: 5px 10px; border-radius: 10px; background: var(--surface-2); border: 1px solid var(--line); color: var(--ink-2); font-size: .84rem; min-width: 0; }
.tp-index a b { font-family: var(--font-mono); color: var(--ink); }
.tp-index a:hover { border-color: var(--coral); }
.tp-index a.done { border-color: color-mix(in srgb, var(--good) 45%, var(--line)); }
.tp-index a.done b::after { content: " ✓"; color: var(--good); }
.tp-list { display: grid; gap: 22px; grid-template-columns: minmax(0, 1fr); }
.tp-ex { display: grid; gap: 16px; padding: 0; overflow: hidden; scroll-margin-top: 76px; grid-template-columns: minmax(0, 1fr); }
.tp-head { display: grid; grid-template-columns: auto minmax(0, 1fr) auto; gap: 14px; align-items: center; padding: 16px 20px; background: var(--surface-2); border-bottom: 1px solid var(--line); }
.tp-num { min-width: 3.1em; text-align: center; font-family: var(--font-display); font-weight: 800; font-size: 1.05rem; color: #fff; background: var(--grad); padding: 8px 10px; border-radius: 12px; }
.tp-title h2 { font-size: 1.15rem; margin: 0 0 6px; line-height: 1.25; }
.tp-solved { display: flex; gap: 6px; align-items: center; font-weight: 700; font-size: .88rem; cursor: pointer; white-space: nowrap; }
.tp-problem, .tp-solution { padding: 0 20px; display: grid; gap: 8px; min-width: 0; grid-template-columns: minmax(0, 1fr); }
.tp-problem { background: color-mix(in srgb, var(--violet) 6%, var(--surface)); margin: 0 20px; padding: 14px 16px; border-radius: 12px; border-left: 4px solid var(--violet); }
.tp-solution { padding-bottom: 20px; gap: 14px; }
.tp-sol-body { display: grid; gap: 18px; min-width: 0; grid-template-columns: minmax(0, 1fr); }
.tp-blk { min-width: 0; display: grid; gap: 8px; grid-template-columns: minmax(0, 1fr); }
.tp-blk h4 { font-size: .98rem; margin: 0; }
.tp-reveal { padding: 0 20px 20px; display: flex; gap: 12px; align-items: center; flex-wrap: wrap; }
.tp-answer > div { overflow-wrap: anywhere; }
.tp-img { display: block; max-width: 100%; height: auto; border: 1px solid var(--line); border-radius: 10px; background: #fff; }
.chap-no.tp { font-size: 2rem; }
@media (max-width: 560px) {
  .tp-head { grid-template-columns: auto minmax(0, 1fr); padding: 14px 14px; }
  .tp-solved { grid-column: 1 / -1; }
  .tp-problem { margin: 0 12px; }
  .tp-solution, .tp-reveal { padding-left: 12px; padding-right: 12px; }
}

.tp-sol-body .readout span, .tp-sol-body th { text-transform: none; letter-spacing: 0; }
@media (max-width: 480px) {
  .topbar .modes { gap: 2px; padding: 3px; }
  .topbar .modes a { padding: 6px 6px; font-size: .78rem; }
  .topbar .seg button { padding-left: 8px; padding-right: 8px; }
}