:root {
  --bg: #f6f7fb;
  --card: #ffffff;
  --text: #1b1f2a;
  --muted: #5d6578;
  --line: #e2e5ee;
  --accent: #2f5bea;
  --accent-ink: #ffffff;
  --accent-soft: #e8edfe;
  --radius: 14px;
  --good: #1b7f4b; --good-bg: #e6f5ec;
  --bad: #b3261e; --bad-bg: #fdeceb;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-mode="light"]) {
    --bg: #0f1218;
    --card: #181c25;
    --text: #e8ebf3;
    --muted: #9aa3b8;
    --line: #272d3a;
    --accent: #7b9bff;
    --accent-ink: #0f1218;
    --accent-soft: #1f2842;
    --good: #5fd08f; --good-bg: #14301f;
    --bad: #ff8a80; --bad-bg: #3a1a18;
  }
}
:root[data-mode="dark"] {
    --bg: #0f1218;
    --card: #181c25;
    --text: #e8ebf3;
    --muted: #9aa3b8;
    --line: #272d3a;
    --accent: #7b9bff;
    --accent-ink: #0f1218;
    --accent-soft: #1f2842;
    --good: #5fd08f; --good-bg: #14301f;
    --bad: #ff8a80; --bad-bg: #3a1a18;
  }

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
html[data-text="lg"] { font-size: 112.5%; }
html[data-text="xl"] { font-size: 125%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 1rem/1.55 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}
a { color: var(--accent); }
.wrap { max-width: 980px; margin: 0 auto; padding: 0 16px; }

header.site {
  background: var(--card);
  border-bottom: 1px solid var(--line);
}
header.site .wrap {
  display: flex; align-items: center; justify-content: space-between;
  gap: 12px; padding-top: 14px; padding-bottom: 14px; flex-wrap: wrap;
}
.brand { font-weight: 700; font-size: 1.15rem; color: var(--text); text-decoration: none; }
nav.top { display: flex; gap: 8px; flex-wrap: wrap; }

.btn {
  display: inline-block; padding: 8px 14px; border-radius: 10px;
  border: 1px solid var(--line); background: var(--card); color: var(--text);
  text-decoration: none; font-size: .92rem; cursor: pointer; font-family: inherit;
}
.btn:hover { border-color: var(--accent); }
.btn.primary { background: var(--accent); color: var(--accent-ink); border-color: var(--accent); font-weight: 600; }

.hero { padding: 36px 0 12px; }
.hero h1 { margin: 0 0 6px; font-size: clamp(1.7rem, 5vw, 2.4rem); line-height: 1.15; }
.hero p { margin: 0; color: var(--muted); font-size: 1.05rem; }
.hero .actions { margin-top: 18px; display: flex; gap: 10px; flex-wrap: wrap; }

h2.section { margin: 30px 0 12px; font-size: 1.15rem; }

.grid { display: grid; gap: 14px; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); }
.card {
  background: var(--card); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 16px;
}
a.unit-card { display: block; text-decoration: none; color: inherit; transition: border-color .15s, transform .15s; }
a.unit-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.unit-card h3 { margin: 0 0 6px; font-size: 1.05rem; }
.unit-card p { margin: 0 0 12px; color: var(--muted); font-size: .93rem; }
.chips { display: flex; gap: 6px; flex-wrap: wrap; }
.chip { font-size: .78rem; background: var(--accent-soft); color: var(--accent); padding: 3px 9px; border-radius: 999px; }

.crumbs { margin: 22px 0 4px; font-size: .9rem; }
.unit-head h1 { margin: 4px 0 6px; font-size: clamp(1.6rem, 5vw, 2.1rem); }
.unit-head p { margin: 0; color: var(--muted); }

.list { display: grid; gap: 10px; }
.row {
  background: var(--card); border: 1px solid var(--line); border-radius: 12px;
  padding: 12px 14px;
}
.row-top { display: flex; align-items: center; justify-content: space-between; gap: 10px; flex-wrap: wrap; }
.row-title { font-weight: 600; }
.row-actions { display: flex; gap: 8px; flex-wrap: wrap; }
.viewer { margin-top: 12px; }
.viewer iframe { width: 100%; height: min(78vh, 720px); border: 1px solid var(--line); border-radius: 10px; background: #fff; }

.videos { display: grid; gap: 14px; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); }
.video { background: var(--card); border: 1px solid var(--line); border-radius: 12px; overflow: hidden; }
.video .frame { position: relative; aspect-ratio: 16 / 9; background: #000; }
.video iframe, .video button.thumb { position: absolute; inset: 0; width: 100%; height: 100%; border: 0; }
.video button.thumb { padding: 0; cursor: pointer; background: #000 center / cover no-repeat; }
.video button.thumb::after {
  content: "▶"; position: absolute; left: 50%; top: 50%; transform: translate(-50%, -50%);
  width: 58px; height: 58px; border-radius: 50%; background: rgba(0,0,0,.65); color: #fff;
  display: grid; place-items: center; font-size: 22px; padding-left: 4px;
}
.video .cap { padding: 10px 12px; font-weight: 600; font-size: .95rem; }
.playlist { aspect-ratio: 16 / 9; width: 100%; border: 0; border-radius: 12px; background: #000; }

.empty { color: var(--muted); font-size: .93rem; padding: 14px; border: 1px dashed var(--line); border-radius: 12px; }
footer.site { margin: 48px 0 28px; color: var(--muted); font-size: .85rem; text-align: center; }

/* --- additions: unit numbers, video groups, links --- */
.eyebrow { font-size: .78rem; font-weight: 600; letter-spacing: .06em; text-transform: uppercase; color: var(--accent); margin-bottom: 4px; }
.unit-head .eyebrow { margin-top: 10px; }
.group-label { margin: 18px 0 10px; font-size: .95rem; font-weight: 600; color: var(--muted); }
.video .cap { display: flex; justify-content: space-between; align-items: baseline; gap: 10px; }
.video .cap a { font-size: .8rem; font-weight: 400; white-space: nowrap; }
.section-link { margin: 0 0 4px; font-size: .9rem; }

/* --- study tools: start here, equations, quiz --- */
.unit-nav { display: flex; gap: 8px; flex-wrap: wrap; margin: 18px 0 4px; position: sticky; top: 0; z-index: 5; background: var(--bg); padding: 8px 0; border-bottom: 1px solid var(--line); }
.navchip { font: inherit; font-size: .85rem; padding: 6px 12px; border-radius: 999px; border: 1px solid var(--line); background: var(--card); color: var(--text); cursor: pointer; }
.navchip:hover { border-color: var(--accent); color: var(--accent); }
section[id] { scroll-margin-top: 64px; }
.sec-head { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.startbox { background: var(--card); border: 1px solid var(--line); border-left: 4px solid var(--accent); border-radius: var(--radius); padding: 4px 18px 18px; margin-top: 18px; }
h2.section.first { margin-top: 14px; }
.start-lead { margin: 0 0 10px; color: var(--muted); }
h3.sub { margin: 20px 0 8px; font-size: .95rem; }
.startbox .goto.primary { text-align: left; }
.helps { list-style: none; margin: 0; padding: 0; display: grid; gap: 8px; }
.linkbtn { width: 100%; display: flex; justify-content: space-between; align-items: baseline; gap: 12px; flex-wrap: wrap; text-align: left; font: inherit; padding: 10px 12px; border-radius: 10px; border: 1px solid var(--line); background: var(--bg); color: var(--text); cursor: pointer; }
.linkbtn:hover { border-color: var(--accent); }
.linkbtn .go { font-size: .82rem; color: var(--accent); }
.mistakes { margin: 0; padding-left: 20px; display: grid; gap: 8px; }
.eq-grid { display: grid; gap: 10px; }
.eq-row { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 10px 14px; }
.eq-name { font-weight: 600; font-size: .9rem; color: var(--muted); }
.eq-math { overflow-x: auto; overflow-y: hidden; }
.eq-math .katex-display { margin: .4em 0; text-align: left; }
.eq-math .katex-display > .katex { text-align: left; }
.eq-note { font-size: .88rem; color: var(--muted); }
.consts { display: grid; gap: 6px; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); }
.const { display: flex; justify-content: space-between; gap: 10px; background: var(--card); border: 1px solid var(--line); border-radius: 10px; padding: 8px 12px; font-size: .9rem; }
.const .cn { color: var(--muted); }
.print-only { display: none; }
.quiz-intro { margin: 0 0 12px; color: var(--muted); font-size: .93rem; }
.quiz-score { font-weight: 600; color: var(--accent); }
.quiz-q { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 14px; margin-bottom: 12px; }
.qtext { font-weight: 600; margin-bottom: 10px; }
.qnum { color: var(--accent); }
.choices { display: grid; gap: 8px; }
.choice { text-align: left; font: inherit; padding: 10px 12px; border-radius: 10px; border: 1px solid var(--line); background: var(--bg); color: var(--text); cursor: pointer; }
.choice:hover:not(:disabled) { border-color: var(--accent); }
.choice:disabled { cursor: default; }
.choice.right { border-color: var(--good); background: var(--good-bg); }
.choice.wrong { border-color: var(--bad); background: var(--bad-bg); }
.feedback { margin-top: 10px; padding: 10px 12px; border-radius: 10px; font-size: .93rem; }
.feedback.good { background: var(--good-bg); }
.feedback.bad { background: var(--bad-bg); }
.quiz-done { margin-top: 6px; padding: 12px 14px; border-radius: 12px; border: 1px dashed var(--line); display: flex; gap: 12px; align-items: center; flex-wrap: wrap; }
@media print {
  body.printing-eq header.site, body.printing-eq footer.site, body.printing-eq .crumbs, body.printing-eq .unit-head,
  body.printing-eq .unit-nav, body.printing-eq main > section:not(#sec-equations), body.printing-eq .noprint { display: none !important; }
  body.printing-eq { background: #fff; color: #000; }
  body.printing-eq .print-only { display: block; font-weight: 700; font-size: 1.1rem; margin-bottom: 8px; }
  body.printing-eq .eq-row, body.printing-eq .const { break-inside: avoid; border-color: #bbb; background: #fff; }
  body.printing-eq .eq-name, body.printing-eq .eq-note, body.printing-eq .const .cn { color: #333; }
}
.eq-grid { grid-template-columns: minmax(0, 1fr); }
.eq-row { min-width: 0; }
.eq-math .katex-display > .katex { white-space: normal; }
.consts .const { min-width: 0; }
@media (max-width: 640px) {
  .unit-nav { flex-wrap: nowrap; overflow-x: auto; -webkit-overflow-scrolling: touch; }
  .navchip { white-space: nowrap; flex: 0 0 auto; }
}

/* --- home page login --- */
.hero-split { display: grid; gap: 24px; grid-template-columns: minmax(0, 1.2fr) minmax(0, 1fr); align-items: start; }
.hero-split .hero-text { padding-top: 6px; }
form.login { margin: 0; }
form.login h2 { margin: 0 0 4px; font-size: 1.1rem; }
.login-sub { margin: 0 0 12px; color: var(--muted); font-size: .9rem; }
form.login label { display: block; font-size: .85rem; font-weight: 600; margin: 10px 0 4px; }
form.login input[type="text"], form.login input[type="password"] {
  width: 100%; font: inherit; padding: 10px 12px; border-radius: 10px; border: 1px solid var(--line);
  background: var(--bg); color: var(--text);
}
form.login input:focus-visible, .navchip:focus-visible, .btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
form.login label.showpw { font-weight: 400; display: flex; gap: 8px; align-items: center; margin-top: 8px; }
.login-btn { width: 100%; margin-top: 14px; font-size: 1rem; padding: 10px 14px; }
.login-help { margin: 12px 0 0; font-size: .85rem; }
@media (max-width: 760px) { .hero-split { grid-template-columns: minmax(0, 1fr); } }

/* --- worked examples --- */
.worked { background: var(--card); border: 1px solid var(--line); border-left: 4px solid var(--accent); border-radius: var(--radius); padding: 14px 16px; margin-bottom: 14px; }
.worked-head { display: flex; justify-content: space-between; align-items: center; gap: 10px; flex-wrap: wrap; }
.worked-topic { font-weight: 700; }
.wprob { margin: 10px 0; }
details.wsol { border-top: 1px dashed var(--line); padding-top: 8px; }
details.wsol summary { cursor: pointer; color: var(--accent); font-weight: 600; padding: 4px 0; }
details.wsol summary:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.wsteps p { margin: 8px 0; }
.weq { overflow-x: auto; overflow-y: hidden; margin: 2px 0; }
.weq .katex-display { margin: .5em 0; text-align: left; }
.weq .katex-display > .katex { text-align: left; }
.wans { background: var(--good-bg); border-radius: 10px; padding: 10px 12px; margin-top: 10px; }
@media print { .worked { break-inside: avoid; } }

/* ===== search ===== */
.search { margin: 26px 0 4px; }
.search-label { display: block; font-weight: 600; margin-bottom: 6px; }
.search input[type=search] { width: 100%; font: inherit; font-size: 1.05rem; padding: 12px 14px; border: 1.5px solid var(--line); border-radius: 10px; background: var(--card); color: var(--text); }
.search input[type=search]:focus { outline: 3px solid var(--accent-soft); border-color: var(--accent); }
.results { margin-top: 8px; }
.result-list { list-style: none; margin: 0 0 10px; padding: 0; display: grid; gap: 6px; }
.result { display: flex; gap: 12px; align-items: baseline; width: 100%; text-align: left; font: inherit; color: var(--text); text-decoration: none; background: var(--card); border: 1px solid var(--line); border-radius: 10px; padding: 9px 12px; cursor: pointer; }
.result:hover, .result:focus-visible { border-color: var(--accent); }
.rtype { flex: none; min-width: 5.6rem; font-size: .78rem; font-weight: 600; color: var(--accent); }
.rmain { display: flex; flex-direction: column; min-width: 0; }
.rtitle { font-weight: 600; overflow-wrap: anywhere; }
.rwhere { font-size: .8rem; color: var(--muted); }
.no-results { color: var(--muted); margin: 6px 0; }
@media (max-width: 520px) { .result { flex-direction: column; gap: 2px; } }

/* ===== progress ===== */
.uprog { margin-top: 12px; font-size: .8rem; color: var(--muted); }
.uprog .bar { display: block; height: 5px; background: var(--line); border-radius: 3px; overflow: hidden; margin-bottom: 4px; }
.uprog .bar i { display: block; height: 100%; background: var(--good); }
.saved-note { margin: 28px 0 8px; font-size: .85rem; color: var(--muted); }
.linkbtn-inline { font: inherit; background: none; border: 0; padding: 0; color: var(--accent); text-decoration: underline; cursor: pointer; text-align: left; }
.video .cap { align-items: center; }
.cap-actions { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; justify-content: flex-end; }
.mark { font: inherit; font-size: .78rem; padding: 3px 9px; border-radius: 999px; border: 1px solid var(--line); background: var(--bg); color: var(--muted); cursor: pointer; font-weight: 400; }
.mark[aria-pressed="true"] { background: var(--good-bg); color: var(--good); border-color: var(--good); font-weight: 600; }
.video.is-watched { border-color: var(--good); }
.head-actions { display: flex; gap: 14px; align-items: center; flex-wrap: wrap; margin-top: 12px !important; }
.watch-count { font-size: .88rem; color: var(--muted); }

/* ===== quiz review links ===== */
.fixit { margin-top: 10px; display: flex; gap: 8px; flex-wrap: wrap; align-items: center; }
.fixit-label { font-weight: 600; font-size: .88rem; }
.fixit .btn { font-size: .85rem; text-align: left; }

/* ===== test review page ===== */
.rv-steps { margin: 16px 0 6px; padding-left: 1.3rem; display: grid; gap: 4px; }
.rv-note { color: var(--muted); font-size: .92rem; margin: 6px 0 0; }

/* ===== tools ===== */
.tool { padding: 18px; margin: 16px 0; }
.tool h2 { margin: 0 0 12px; font-size: 1.1rem; }
.tool-row { display: flex; gap: 12px; flex-wrap: wrap; align-items: end; }
.tool-row label { display: grid; gap: 4px; font-size: .85rem; font-weight: 600; min-width: 0; }
.tool-row label.grow { flex: 1 1 160px; }
.tool-row input, .tool-row select { font: inherit; font-size: 1rem; padding: 9px 10px; border: 1.5px solid var(--line); border-radius: 8px; background: var(--bg); color: var(--text); min-width: 0; max-width: 100%; }
.tool-row input:focus, .tool-row select:focus { outline: 3px solid var(--accent-soft); border-color: var(--accent); }
.tool-out { margin-top: 14px; font-size: 1.15rem; overflow-wrap: anywhere; }
.tool-sub { font-size: .88rem; color: var(--muted); margin-top: 4px; font-weight: 400; }
.tool-hint { font-size: .85rem; color: var(--muted); margin: 12px 0 0; }
.sf-show { font: 600 1.9rem/1.2 ui-monospace, "SF Mono", Menlo, Consolas, monospace; margin-bottom: 6px; letter-spacing: .02em; overflow-wrap: anywhere; }
.sf-d { color: var(--muted); opacity: .55; }
.sf-d.is-sig { color: var(--text); opacity: 1; background: var(--accent-soft); border-radius: 3px; padding: 0 1px; }
.sf-exp { font-size: 1.2rem; color: var(--text); }

/* ===== how to ===== */
.howto-grid { display: grid; gap: 14px; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); margin-top: 18px; }
.how { padding: 16px 18px; }
.how h3 { margin: 0 0 6px; font-size: 1.02rem; }
.how p { margin: 0; font-size: .95rem; }
.how.install { margin-top: 14px; }
kbd { font: .85em ui-monospace, Menlo, monospace; border: 1px solid var(--line); border-bottom-width: 2px; border-radius: 4px; padding: 0 5px; background: var(--card); }
.qr { flex: none; width: 150px; text-align: center; font-size: .72rem; color: var(--muted); margin-left: auto; }
.qr svg { width: 100%; height: auto; display: block; background: #fff; border-radius: 6px; }
.howto-actions { margin: 20px 0; display: flex; gap: 10px; flex-wrap: wrap; }
#poster { display: none; }
@media (max-width: 640px) { .unit-head .qr { display: none; } }

@media print {
  body.printing-howto header.site, body.printing-howto footer.site, body.printing-howto .noprint, body.printing-howto #poster,
  body.printing-poster header.site, body.printing-poster footer.site, body.printing-poster main > :not(#poster) { display: none !important; }
  body.printing-howto, body.printing-poster { background: #fff !important; color: #000; }
  body.printing-howto .unit-head, body.printing-howto .card { box-shadow: none !important; background: #fff !important; break-inside: avoid; }
  body.printing-howto .unit-head .qr { display: block !important; }
  body.printing-howto .howto-grid { gap: 8px; grid-template-columns: 1fr 1fr; }
  body.printing-howto { font-size: 12px; }
  body.printing-howto .unit-head h1 { font-size: 1.6rem; }
  body.printing-poster #poster { display: flex !important; flex-direction: column; align-items: center; text-align: center; gap: 8px; padding-top: 10px; }
  body.printing-poster #poster h1 { font-size: 3rem; margin: 0; }
  body.printing-poster .poster-qr { width: 62%; max-width: 420px; }
  body.printing-poster .poster-qr svg { width: 100%; height: auto; }
  body.printing-poster .poster-scan { font-size: 1.6rem; font-weight: 700; margin: 8px 0 0; }
  body.printing-poster .poster-url { font-size: 1.2rem; margin: 0; word-break: break-all; }
}
.brand { display: inline-flex; align-items: center; gap: 10px; }
.brand-mark { width: 34px; height: 34px; border-radius: 8px; display: block; }
#poster .poster-logo { width: 30%; max-width: 200px; border-radius: 28px; }

/* ===== progress card, badges, toast ===== */
.myprog { padding: 16px 18px; margin: 22px 0 6px; }
.mp-title { margin: 0 0 12px; font-size: 1.05rem; }
.mp-stats { display: grid; grid-template-columns: repeat(auto-fit, minmax(120px, 1fr)); gap: 10px; }
.stat { display: flex; flex-direction: column; background: var(--bg); border: 1px solid var(--line); border-radius: 10px; padding: 10px 12px; }
.stat-n { font-size: 1.7rem; font-weight: 700; line-height: 1.1; }
.stat-n small { font-size: .85rem; font-weight: 400; color: var(--muted); }
.stat-l { font-size: .8rem; color: var(--muted); }
.mp-hint { margin: 12px 0 0; font-size: .88rem; color: var(--muted); }
.mp-weak { margin: 12px 0 0; font-size: .92rem; }
.badges { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 12px; }
.badge { font-size: .78rem; padding: 3px 10px; border-radius: 999px; border: 1px dashed var(--line); color: var(--muted); }
.badge.earned { border: 1px solid var(--good); background: var(--good-bg); color: var(--good); font-weight: 600; }
.chip-done { background: var(--good-bg); color: var(--good); font-weight: 600; }
.unit-status { margin: 8px 0 0 !important; font-size: .88rem; color: var(--muted); }
.done-badge { display: inline-block; background: var(--good-bg); color: var(--good); border: 1px solid var(--good); border-radius: 999px; padding: 1px 10px; font-weight: 700; margin-right: 6px; }
.toast { position: fixed; left: 50%; bottom: 22px; transform: translateX(-50%); z-index: 50; max-width: min(92vw, 420px); background: var(--text); color: var(--bg); padding: 12px 18px; border-radius: 12px; box-shadow: 0 10px 30px rgba(0,0,0,.3); font-weight: 600; font-size: .95rem; animation: toast-in .25s ease-out; }
@keyframes toast-in { from { opacity: 0; transform: translate(-50%, 10px); } to { opacity: 1; transform: translate(-50%, 0); } }
@media (prefers-reduced-motion: reduce) { .toast { animation: none; } }

/* ===== quick links, setup forms ===== */
.quick { display: grid; gap: 12px; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); margin: 14px 0 0; }
.quick-link { display: flex; flex-direction: column; gap: 3px; padding: 12px 14px; background: var(--card); border: 1px solid var(--line); border-radius: 12px; text-decoration: none; color: var(--text); }
.quick-link span { font-size: .85rem; color: var(--muted); }
.quick-link:hover, .quick-link:focus-visible { border-color: var(--accent); }
.setup { padding: 18px; margin: 16px 0; }
.setup fieldset { border: 0; margin: 14px 0; padding: 0; min-width: 0; }
.setup legend { font-weight: 700; margin-bottom: 8px; padding: 0; }
.opt { display: flex; gap: 8px; align-items: baseline; margin: 6px 0; }
.mx-units { margin: 4px 0 8px 24px; display: grid; gap: 2px; }
.reasons { display: grid; gap: 8px; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); }
.reason { display: flex; gap: 10px; align-items: flex-start; padding: 10px 12px; border: 1px solid var(--line); border-radius: 10px; background: var(--bg); cursor: pointer; }
.reason:has(input:checked) { border-color: var(--accent); background: var(--accent-soft); }
.reason small { display: block; color: var(--muted); font-size: .82rem; margin-top: 2px; }
.reason input { margin-top: 4px; }
.plan { padding: 16px 18px; margin: 12px 0; }
.plan h2 { margin: 0 0 6px; font-size: 1.05rem; }
.plan p { margin: 0 0 4px; }
.qunit { font-size: .8rem; color: var(--muted); margin-bottom: 4px; }
label.block { display: grid; gap: 4px; font-size: .88rem; font-weight: 600; margin: 12px 0; }
.setup textarea { font: inherit; font-size: 1rem; padding: 9px 10px; border: 1.5px solid var(--line); border-radius: 8px; background: var(--bg); color: var(--text); width: 100%; resize: vertical; }
.setup textarea[readonly] { color: var(--muted); }
a.btn[aria-disabled="true"] { opacity: .55; }
.how-link { text-decoration: none; color: var(--text); display: block; }
.how-link:hover, .how-link:focus-visible { border-color: var(--accent); }

/* ===== appearance menu ===== */
header.site .wrap { position: relative; }
.prefs { position: absolute; right: 16px; top: 100%; z-index: 20; background: var(--card); border: 1.5px solid var(--text); border-radius: 12px; padding: 12px 16px; display: grid; gap: 10px; box-shadow: 0 12px 30px rgba(0,0,0,.2); min-width: 220px; }
.prefs[hidden] { display: none; }
.prefs fieldset { border: 0; margin: 0; padding: 0; }
.prefs legend { font-weight: 700; font-size: .85rem; margin-bottom: 4px; padding: 0; }
.prefs label { display: flex; gap: 8px; align-items: center; padding: 3px 0; font-size: .95rem; }
.prefs-btn { font-weight: 700; }
.btn:focus-visible, .choice:focus-visible, .quick-link:focus-visible, .result:focus-visible, .mark:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
@media print {
  body.printing-howto { font-size: 10.5px; line-height: 1.4; }
  body.printing-howto .how { padding: 8px 10px; }
  body.printing-howto .how h3 { font-size: 11.5px; margin-bottom: 3px; }
  body.printing-howto .how p { font-size: 10.5px; }
  body.printing-howto .unit-head { padding: 8px 12px; margin-top: 0; }
  body.printing-howto .unit-head h1 { font-size: 1.35rem; margin: 2px 0; }
  body.printing-howto .qr { width: 100px; }
}
.hp { position: absolute; left: -9999px; width: 1px; height: 1px; overflow: hidden; }
.setup input[type=email] { font: inherit; font-size: 1rem; padding: 9px 10px; border: 1.5px solid var(--line); border-radius: 8px; background: var(--bg); color: var(--text); width: 100%; }
#ak-fallback { margin-top: 14px; }

/* misconception busters */
.sec-intro { margin: -6px 0 10px; color: var(--muted); max-width: 62ch; }
.myth-row .myth-said { margin-top: 8px; padding: 6px 10px; border-left: 4px solid var(--pen, #d23b2f); border-radius: 3px; font-size: .92rem; color: var(--muted); }

/* ================= accessibility + layout pass ================= */
/* 44px tap targets */
.btn, .navchip, .choice, summary.btn, .linkbtn, button.rr-var { min-height: 44px; }
.btn, .navchip { display: inline-flex; align-items: center; justify-content: center; }
.navchip { padding: 8px 14px; }
.crumbs a, .login-help a, .linkbtn-inline, .saved-note button { display: inline-block; padding: 12px 4px; }
.crumbs { margin: 10px 0 0; }
input[type=checkbox], input[type=radio] { width: 22px; height: 22px; flex: none; accent-color: var(--accent); }
label:has(> input[type=checkbox]), label:has(> input[type=radio]), label.opt, .showpw { display: flex; align-items: center; gap: 10px; min-height: 44px; }
.chip, .mark { min-height: 32px; }
.mark { padding: 6px 12px; font-size: .9rem; }
.chip { font-size: .85rem; }
.rtype, .eyebrow { font-size: .85rem; }
.quick-link { min-height: 44px; }

/* header: menu on phones */
.menu-btn { display: none; margin-left: auto; }
@media (max-width: 700px) {
  header.site .wrap { flex-wrap: wrap; align-items: center; }
  .menu-btn { display: inline-flex; }
  nav.top { display: none; width: 100%; order: 3; flex-direction: column; gap: 8px; padding: 8px 0 4px; }
  nav.top.open { display: flex; }
  nav.top .btn { width: 100%; justify-content: flex-start; }
  .prefs { right: 12px; left: 12px; }
}

/* login fold */
.loginfold > summary { list-style: none; cursor: pointer; width: 100%; justify-content: center; font-weight: 700; }
.loginfold > summary::-webkit-details-marker { display: none; }
.loginfold[open] > summary { display: none; }
@media (max-width: 899px) { .loginfold[open] > summary { display: inline-flex; margin-bottom: 8px; } .hero-split { grid-template-columns: 1fr !important; } }

/* next step / due cards */
.nextcard, .duecard { margin: 14px 0; border-left: 6px solid var(--accent); }
.duecard { border-left-color: var(--pen, #d23b2f); }
.next-row { display: flex; gap: 12px; align-items: center; justify-content: space-between; flex-wrap: wrap; }
.next-label { font-size: .85rem; color: var(--muted); font-weight: 600; }
.next-text { font-size: 1.05rem; font-weight: 600; margin-top: 2px; }
.tw-note { margin: 0 0 10px; }

/* collapsible unit sections */
details.fold { margin: 6px 0; }
details.fold > summary { list-style: none; cursor: pointer; display: flex; align-items: center; gap: 10px; min-height: 52px; padding: 8px 14px; border: 1.5px solid var(--line); border-radius: 10px; background: var(--card); }
details.fold > summary::-webkit-details-marker { display: none; }
details.fold > summary:hover { border-color: var(--accent); }
.fold-title { font-weight: 700; font-size: 1.15rem; }
.fold-count { font-size: .85rem; background: var(--accent-soft); color: var(--accent); border-radius: 999px; padding: 2px 10px; font-weight: 600; }
.fold-hint { margin-left: auto; width: 12px; height: 12px; border-right: 3px solid var(--muted); border-bottom: 3px solid var(--muted); transform: rotate(45deg); transition: transform .15s; }
details.fold[open] > summary .fold-hint { transform: rotate(-135deg); }
details.fold[open] > summary { margin-bottom: 12px; }
@media print { details.fold > summary { display: none; } }
@media (prefers-reduced-motion: reduce) { .fold-hint { transition: none; } }
.unit-nav { margin-top: 12px; }

/* symbols + hints + listen + glossary */
details.symbols { margin: 8px 0 12px; }
details.symbols > summary { cursor: pointer; font-weight: 600; min-height: 44px; display: flex; align-items: center; color: var(--accent); }
.symtab { border-collapse: collapse; width: 100%; max-width: 560px; }
.symtab th, .symtab td { text-align: left; padding: 6px 10px; border-bottom: 1px solid var(--line); vertical-align: middle; }
.symtab th { width: 7.5rem; font-weight: 400; }
.sub-row { display: flex; align-items: center; justify-content: space-between; gap: 10px; flex-wrap: wrap; }
.start-tool { margin: 12px 0 0; }
.hintbar { margin: 8px 0 0; display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.hinttext { color: var(--muted); font-size: .95rem; }
.quiz-q.done .hintbar { display: none; }
.choice.ruled-out { text-decoration: line-through; opacity: .5; }
.fb-listen { margin-top: 8px; }
.btn.listen.on { background: var(--accent); color: #fff; border-color: var(--accent); }
.gl { text-decoration: underline dotted; text-decoration-thickness: 2px; text-underline-offset: 3px; cursor: help; }
.gl:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; border-radius: 2px; }
.gl-pop { position: absolute; z-index: 30; width: min(320px, calc(100vw - 16px)); background: var(--card); color: var(--text); border: 2px solid var(--text); border-radius: 8px; padding: 12px 14px; box-shadow: 4px 4px 0 var(--line); }
.gl-pop strong { text-transform: capitalize; font-size: 1.05rem; }
.gl-pop p { margin: 6px 0 10px; }
.gl-actions { display: flex; gap: 8px; }

/* rearranging tool */
.rr-eq { margin: 10px 0; overflow-x: auto; }
.rr-pick { display: flex; flex-wrap: wrap; gap: 8px; }
.rr-var { flex-direction: column; gap: 0; padding: 6px 12px; line-height: 1.2; }
.rr-var[aria-pressed="true"] { background: var(--accent); color: #fff; border-color: var(--accent); }
.rr-word { font-size: .8rem; opacity: .85; font-weight: 400; }
.rr-step { margin: 12px 0; padding: 10px 12px; border-left: 4px solid var(--line); }
.rr-num { font-size: .85rem; color: var(--muted); font-weight: 700; }
.rr-math { overflow-x: auto; }
.rr-say { margin-top: 4px; }
.rr-final { margin: 14px 0; padding: 12px; background: var(--accent-soft); border-radius: 8px; overflow-x: auto; }
.rr-fields { display: grid; gap: 10px; grid-template-columns: repeat(auto-fit, minmax(190px, 1fr)); }
.rr-fields label { display: flex; flex-direction: column; gap: 4px; }
.rr-q { margin: 14px 0 6px; }
.cap-actions { display: flex; gap: 8px; align-items: center; flex-wrap: wrap; }
.cap-actions .mark, .cap-actions a { min-height: 44px; display: inline-flex; align-items: center; padding: 6px 14px; }
.brand { min-height: 44px; display: inline-flex; align-items: center; }
.login-help a, .sec-intro a, .start-tool a { padding: 10px 2px; display: inline-block; }
@media (max-width: 700px) { .hero-deco { display: none; } }
summary { min-height: 44px; padding-top: 10px; padding-bottom: 10px; }
details.symbols > summary, details.fold > summary { display: flex; }
p a[href*="youtube.com/playlist"], p a[href*="list="] { display: inline-block; padding: 12px 2px; }
@media (max-width: 700px) { body .hero-deco { display: none !important; } .hero .actions { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; } .hero .actions .btn { width: 100%; text-align: center; } }
select, input[type=text], input[type=number], input[type=search], textarea { min-height: 44px; }
.wk-list { list-style: none; margin: 8px 0 0; padding: 0; display: grid; gap: 8px; }
.wk-list li { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.wk-check { width: 22px; text-align: center; color: var(--good, #1b7f4b); font-weight: 700; }
.wk-title { flex: 1 1 14rem; font-weight: 600; }
.wk-title.done { color: var(--muted); }
.wk-refs { margin-bottom: 14px; } .wk-refs .wk-title { flex: 1 1 200px; }