:root {
  --paper: #f1ece2; --card: #faf6ed; --ink: #2b2721; --soft: #6b6455; --line: #d9d0be; --wash: #ebe3d3;
  --accent: #a8552a; --accent-ink: #fff8f0; --go: #a8552a; --go-ink: #fff8f0;
  --good: #2f6b4f; --bad: #9c3b2e; --good-wash: #e3ede5; --bad-wash: #f3e3df;
  --math: #2f5d8a; --econ: #b07a1c; --cs: #2f6b4f; --humanities: #9c3b2e; --general: #6a4f8f; --other: #6f6858;
  --code: #efe8da; --tk: #8a3b8f; --ts: #2f6b4f; --tc: #8b8473; --tn: #a8552a;
  --serif: "Songti SC", "Noto Serif CJK SC", "Source Han Serif SC", serif;
  --sans: -apple-system, "PingFang SC", "Noto Sans CJK SC", "Microsoft YaHei", sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  --radius: 14px;
}
/* Dark: text a step below full brightness on a ground a step above black, and no large bright fills, to ease long reading. */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) { --paper: #1b1a16; --card: #24221c; --ink: #d9d3c5; --soft: #9e9684; --line: #38342a; --wash: #2c2921;
    --accent: #cf8f62; --accent-ink: #1b140c; --go: #7d5237; --go-ink: #f1e8db;
    --good: #7fbd9c; --bad: #dc8d80; --good-wash: #212d26; --bad-wash: #33231f;
    --math: #7fa9d4; --econ: #d6ad5f; --cs: #7fbd9c; --humanities: #dc8d80; --general: #b3a0d2; --other: #9e9684;
    --code: #1f1d18; --tk: #cc9ace; --ts: #8cc8a4; --tc: #7e7867; --tn: #dba074; color-scheme: dark; }
}
:root[data-theme="dark"] { --paper: #1b1a16; --card: #24221c; --ink: #d9d3c5; --soft: #9e9684; --line: #38342a; --wash: #2c2921;
  --accent: #cf8f62; --accent-ink: #1b140c; --go: #7d5237; --go-ink: #f1e8db;
  --good: #7fbd9c; --bad: #dc8d80; --good-wash: #212d26; --bad-wash: #33231f;
  --math: #7fa9d4; --econ: #d6ad5f; --cs: #7fbd9c; --humanities: #dc8d80; --general: #b3a0d2; --other: #9e9684;
  --code: #1f1d18; --tk: #cc9ace; --ts: #8cc8a4; --tc: #7e7867; --tn: #dba074; color-scheme: dark; }
* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--paper); color: var(--ink); font: 17px/1.8 var(--sans); zoom: var(--zoom, 1); }
main { max-width: 680px; margin: 0 auto; padding: calc(16px + env(safe-area-inset-top)) 18px calc(160px + env(safe-area-inset-bottom)); }
body.listening main { padding-top: calc(104px + env(safe-area-inset-top)); }
.player { position: fixed; top: 0; left: 0; right: 0; z-index: 30; padding: calc(4px + env(safe-area-inset-top)) 12px 6px; background: var(--card); border-bottom: 1px solid var(--line); }
.player .prow { display: flex; align-items: center; gap: 6px; max-width: 680px; margin: 0 auto; }
.player button { background: none; border: 0; color: var(--ink); font-size: 18px; min-width: 40px; min-height: 40px; }
.player .pp { color: var(--accent); }
.player .prate, .player .pback { font-size: 14px; font-weight: 600; color: var(--soft); min-width: 48px; font-variant-numeric: tabular-nums; }
.player .ptitle { flex: 1; min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; font-size: 15px; }
.player .ptitle small { color: var(--soft); }
.player input[type="range"] { flex: 1; min-width: 0; accent-color: var(--accent); height: 28px; }
.player .ptime { font-size: 13.5px; color: var(--soft); font-variant-numeric: tabular-nums; white-space: nowrap; }
.pill.listen { margin: 4px 0 8px; }
h1 { font: 700 28px/1.35 var(--serif); margin: 4px 0 14px; letter-spacing: .01em; }
h2 { font: 600 14px/1.4 var(--sans); color: var(--soft); margin: 28px 0 10px; letter-spacing: .1em; }
h3 { font: 600 13px/1.4 var(--sans); color: var(--soft); margin: 0 0 6px; letter-spacing: .12em; }
p { margin: 0 0 14px; }
a { color: var(--accent); }
button { font: inherit; color: inherit; cursor: pointer; }
.note { color: var(--soft); font-size: 15px; }
.loading { margin-top: 30vh; text-align: center; }

/* ── today ─────────────────────────────────────────── */
.top { display: flex; justify-content: space-between; align-items: center; color: var(--soft); font-size: 14px; letter-spacing: .06em; }
.streak { color: var(--accent); font-weight: 600; }
.tiles { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin: 6px 0 14px; }
.tile { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px 16px; display: flex; flex-direction: column; }
.tile b { font: 700 34px/1.1 var(--serif); }
.tile span { font-size: 15px; }
.tile small { color: var(--soft); font-size: 13.5px; line-height: 1.5; margin-top: 4px; }
.done { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 18px; margin: 6px 0 14px; }
.big { font: 700 22px/1.4 var(--serif); margin: 0 0 6px; }
.intro > p { color: var(--soft); }
.list { display: grid; gap: 8px; }
.mini { display: grid; grid-template-columns: 1fr auto; gap: 2px 10px; align-items: baseline; text-align: left; background: var(--card);
  border: 1px solid var(--line); border-left: 4px solid var(--c, var(--other)); border-radius: 12px; padding: 10px 14px; }
.mini small { color: var(--soft); font-size: 13px; }
.mini .progress { grid-column: 1 / -1; }

/* ── progress and tracks ───────────────────────────── */
.progress { display: flex; height: 6px; border-radius: 99px; background: var(--wash); overflow: hidden; margin-top: 6px; }
.progress .m { background: var(--good); }
.progress .l { background: var(--accent); opacity: .55; }
.t-math { --c: var(--math); } .t-econ { --c: var(--econ); } .t-cs { --c: var(--cs); }
.t-humanities { --c: var(--humanities); } .t-general { --c: var(--general); } .t-other { --c: var(--other); }

/* ── courses ───────────────────────────────────────── */
.search { width: 100%; font: inherit; padding: 11px 16px; border-radius: 99px; border: 1.5px solid var(--line); background: var(--card); color: var(--ink); }
.results { display: grid; gap: 6px; margin-top: 10px; }
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(150px, 1fr)); gap: 10px; }
.course { text-align: left; background: var(--card); border: 1px solid var(--line); border-top: 4px solid var(--c); border-radius: var(--radius);
  padding: 12px 14px; display: flex; flex-direction: column; min-height: 92px; }
.course .head { display: flex; justify-content: space-between; align-items: flex-start; gap: 6px; }
.course b { font: 700 17px/1.4 var(--serif); }
.course small { color: var(--soft); font-size: 13.5px; margin-top: auto; }
.badge { font-size: 12px; color: var(--c); border: 1px solid currentColor; border-radius: 99px; padding: 0 7px; white-space: nowrap; line-height: 1.7; }
.back { display: block; background: none; border: 0; color: var(--soft); padding: 4px 0; font-size: 15px; }
.basis { color: var(--soft); font-size: 13px; }
.summary { margin: 10px 0 4px; }
.summary small { color: var(--soft); font-size: 13px; }
.actions { display: flex; flex-wrap: wrap; gap: 8px; margin: 14px 0 6px; }
.pill { background: var(--card); border: 1.5px solid var(--line); border-radius: 99px; padding: 7px 16px; font-size: 15px; font-weight: 600; }
.pill.on { border-color: var(--good); color: var(--good); }
.pill.strong { background: var(--go); border-color: var(--go); color: var(--go-ink); }
.unit { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); margin: 10px 0; overflow: hidden; }
.unit summary { list-style: none; display: flex; justify-content: space-between; align-items: baseline; padding: 12px 16px; font-weight: 600; cursor: pointer; }
.unit summary::-webkit-details-marker { display: none; }
.unit summary small { color: var(--soft); font-weight: 400; font-size: 13px; }
.unit[open] summary { border-bottom: 1px solid var(--line); }
.path { padding: 4px 0; }
.row { display: grid; grid-template-columns: 22px 1fr auto; align-items: center; gap: 8px; width: 100%; text-align: left; background: none;
  border: 0; padding: 8px 16px; position: relative; }
.results .row { background: var(--card); border: 1px solid var(--line); border-radius: 12px; }
.row .label small { display: block; color: var(--soft); font-size: 13.5px; line-height: 1.3; }
.row .state { font-size: 13.5px; color: var(--soft); }
.path .row:not(:last-child)::after { content: ""; position: absolute; left: 26px; top: 30px; bottom: -10px; width: 2px; background: var(--line); }
.dot { width: 12px; height: 12px; border-radius: 50%; border: 2px solid var(--soft); background: var(--paper); justify-self: center; z-index: 1; display: inline-block; }
.s-locked .dot { border-style: dashed; opacity: .5; } .s-locked .label { opacity: .55; }
.s-learning .dot { border-color: var(--accent); background: var(--accent); }
.s-due .dot { border-color: var(--accent); background: var(--paper); box-shadow: 0 0 0 3px var(--wash); }
.s-due .state { color: var(--accent); font-weight: 600; }
.s-mastered .dot { border-color: var(--good); background: var(--good); } .s-mastered .state { color: var(--good); }
.s-skipped .dot { border-color: var(--good); background: var(--good-wash); }
.legend { display: flex; flex-wrap: wrap; gap: 6px 14px; color: var(--soft); font-size: 13px; margin-top: 14px; }
.legend span { display: inline-flex; align-items: center; gap: 6px; }

/* ── studying ──────────────────────────────────────── */
.studybar { display: grid; grid-template-columns: auto 1fr; gap: 6px 12px; align-items: center; margin-bottom: 14px; }
.studybar .tag { grid-column: 1 / -1; justify-self: start; }
.close { background: none; border: 0; font-size: 26px; line-height: 1; color: var(--soft); padding: 0 4px; }
.meter { height: 6px; border-radius: 99px; background: var(--wash); overflow: hidden; }
.meter span { display: block; height: 100%; background: var(--accent); transition: width .3s; }
.tag { display: inline-block; font-size: 13px; letter-spacing: .1em; color: var(--accent); border: 1px solid currentColor; border-radius: 999px; padding: 1px 11px; margin-bottom: 8px; }
.when { font: 700 22px/1.55 var(--serif); margin: 4px 0 14px; }
.facts { list-style: none; margin: 0 0 16px; padding: 0; }
.facts li { padding: 8px 0 8px 14px; border-left: 3px solid var(--line); margin-bottom: 6px; }
.stem { margin-bottom: 4px; }
.passage { margin: 4px 0 16px; padding: 14px 18px; background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); }
.passage blockquote { margin: 0; font: 500 20px/1.9 var(--serif); letter-spacing: .04em; }
.passage figcaption { color: var(--soft); font-size: 13px; margin-top: 8px; }
.terms { display: flex; flex-wrap: wrap; gap: 8px; margin: 0 0 6px; }
.term { background: none; border: 1px dashed var(--soft); border-radius: 8px; padding: 2px 10px; font-size: 14px; color: var(--soft); }
.term[aria-expanded="true"] { border-style: solid; color: var(--ink); }
.plain { background: var(--wash); border-radius: 10px; padding: 10px 14px; font-size: 15px; margin: 6px 0 12px; }
.ask { font: 700 19px/1.55 var(--serif); margin: 16px 0 12px; }
.options { display: grid; gap: 10px; }
.option { display: grid; grid-template-columns: 28px 1fr; gap: 10px; align-items: start; text-align: left; background: var(--card);
  border: 1.5px solid var(--line); border-radius: var(--radius); padding: 12px 14px; min-height: 54px; }
.option .letter { font-style: normal; width: 26px; height: 26px; border-radius: 50%; background: var(--wash); color: var(--soft);
  font-size: 13px; font-weight: 700; display: grid; place-items: center; margin-top: 1px; }
.option .body b { display: block; font-weight: 600; }
.option .body .why { color: var(--soft); font-size: 15.5px; }
.option[aria-pressed="true"] { border-color: var(--accent); box-shadow: inset 0 0 0 1px var(--accent); }
.option[aria-pressed="true"] .letter { background: var(--accent); color: var(--accent-ink); }
.option.right { border-color: var(--good); background: var(--good-wash); } .option.right .letter { background: var(--good); color: var(--card); }
.option.wrong { border-color: var(--bad); background: var(--bad-wash); } .option.wrong .letter { background: var(--bad); color: var(--card); }
.option:disabled { opacity: 1; cursor: default; }
.chips { display: flex; flex-wrap: wrap; gap: 8px; }
.chip { background: var(--card); border: 1.5px solid var(--line); border-radius: 999px; padding: 7px 15px; font-weight: 600; font-size: 15px; }
.chip small { font-weight: 400; color: var(--soft); }
.chip[aria-pressed="true"] { border-color: var(--accent); box-shadow: inset 0 0 0 1px var(--accent); color: var(--accent); }
.verdict { font: 700 21px/1.5 var(--serif); margin: 2px 0 10px; }
.verdict.good { color: var(--good); } .verdict.bad { color: var(--bad); }
.block { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px 16px; margin: 0 0 12px; }
.block.good { border-left: 4px solid var(--good); } .block.bad { border-left: 4px solid var(--bad); }
.block .pick { margin-bottom: 6px; }
.block .pick b { display: block; }
.block .pick .why, .block .pick .text { color: var(--ink); }
.block > :last-child { margin-bottom: 0; }
.block .see { font-size: 14px; }
.lesson { border-left: 4px solid var(--accent); padding: 6px 0 6px 14px; font: 600 18px/1.6 var(--serif); margin: 18px 0; }
.next { color: var(--soft); font-size: 15px; }
.finish { margin-top: 12vh; }
.nextcard { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px 16px; margin-top: 18px; }
.nextcard small { color: var(--soft); display: block; } .nextcard b { font: 700 19px/1.5 var(--serif); }

/* ── the card ──────────────────────────────────────── */
.name { font: 700 34px/1.25 var(--serif); margin: 4px 0 0; }
.en { color: var(--soft); margin: 0 0 14px; letter-spacing: .03em; }
.lead { font-size: 18.5px; line-height: 1.7; }
.analogy { background: var(--wash); border-radius: var(--radius); padding: 12px 16px; margin: 0 0 14px; }
.analogy p { margin: 0; }
.fig { margin: 0 0 16px; }
.fig img { display: block; width: 100%; height: auto; background: #fff; border-radius: var(--radius); }
:root[data-theme="dark"] .fig img { filter: brightness(.86); }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .fig img { filter: brightness(.86); } }
.fig figcaption { color: var(--soft); font-size: 0.9em; margin-top: 6px; text-align: center; }
.excase { font-weight: 700; margin-bottom: 4px; }
.chain { list-style: none; counter-reset: step; margin: 0 0 14px; padding: 0; }
.chain li { counter-increment: step; position: relative; padding: 3px 0 12px 34px; }
.chain li::before { content: counter(step); position: absolute; left: 0; top: 5px; width: 22px; height: 22px; border-radius: 50%;
  background: var(--wash); color: var(--soft); font-size: 13px; line-height: 22px; text-align: center; }
.chain li:not(:last-child)::after { content: ""; position: absolute; left: 10.5px; top: 30px; bottom: 0; width: 1px; background: var(--line); }
.pitfalls { padding-left: 20px; }
.pitfalls li { margin-bottom: 6px; }

/* ── prose: what the content writes in Markdown ────── */
.prose p, .prose ul, .prose ol { margin: 0 0 12px; }
.prose ul, .prose ol { padding-left: 22px; }
.prose li { margin-bottom: 4px; }
.prose h4 { font: 700 17px/1.5 var(--serif); margin: 18px 0 6px; }
.prose blockquote { margin: 0 0 12px; padding: 4px 0 4px 14px; border-left: 3px solid var(--line); color: var(--soft); }
.prose code, .option code, .block code { font: 0.88em var(--mono); background: var(--code); border-radius: 5px; padding: 1px 5px; }
.prose pre.code { background: var(--code); border: 1px solid var(--line); border-radius: 10px; padding: 12px 14px; overflow-x: auto; margin: 0 0 12px;
  font: 13.5px/1.6 var(--mono); }
.prose pre.code code { background: none; padding: 0; font: inherit; }
.tk { color: var(--tk); font-weight: 600; } .ts { color: var(--ts); } .tc { color: var(--tc); font-style: italic; } .tn { color: var(--tn); }
.prose .table { overflow-x: auto; margin: 0 0 12px; }
.prose table { border-collapse: collapse; font-size: 15px; min-width: 60%; }
.prose th, .prose td { border: 1px solid var(--line); padding: 6px 10px; text-align: center; }
.prose th { background: var(--wash); font-weight: 600; }
.prose .math { overflow-x: auto; overflow-y: hidden; margin: 0 0 12px; }
.katex { font-size: 1.06em; }
.katex-display { margin: .4em 0; }

/* ── record ────────────────────────────────────────── */
.heat { display: grid; grid-template-rows: repeat(7, 1fr); grid-auto-flow: column; grid-auto-columns: 1fr; gap: 3px; margin: 4px 0 18px; }
.heat i { aspect-ratio: 1; border-radius: 3px; background: var(--wash); }
.heat .l1 { background: color-mix(in srgb, var(--good) 30%, var(--wash)); }
.heat .l2 { background: color-mix(in srgb, var(--good) 55%, var(--wash)); }
.heat .l3 { background: color-mix(in srgb, var(--good) 78%, var(--wash)); }
.heat .l4 { background: var(--good); }
.heat .lf { background: transparent; }
.stat { display: flex; justify-content: space-between; align-items: baseline; border-bottom: 1px solid var(--line); padding: 12px 0; }
.stat b { font: 700 22px var(--serif); }
.stat small { color: var(--soft); margin-left: 8px; }
.quiet { background: none; border: 0; color: var(--soft); text-decoration: underline; padding: 8px; }

/* ── the button bar and the tabs ───────────────────── */
.bar { position: fixed; left: 0; right: 0; bottom: calc(60px + env(safe-area-inset-bottom)); padding: 14px 18px 12px;
  background: linear-gradient(transparent, var(--paper) 28%); display: flex; justify-content: center; align-items: center; gap: 10px; z-index: 5; }
body:has(#tabs[hidden]) .bar { bottom: env(safe-area-inset-bottom); }
.bar[hidden] { display: none; }
.go { width: 100%; max-width: 644px; border: 0; border-radius: var(--radius); padding: 15px; font-weight: 600; font-size: 18px;
  background: var(--go); color: var(--go-ink); }
.go:disabled { background: var(--line); color: var(--soft); }
.bar .quiet { white-space: nowrap; }
#tabs { position: fixed; left: 0; right: 0; bottom: 0; display: flex; background: var(--card); border-top: 1px solid var(--line);
  padding-bottom: env(safe-area-inset-bottom); z-index: 6; }
#tabs[hidden] { display: none; }
#tabs button { flex: 1; background: none; border: 0; padding: 9px 0 10px; font-size: 13px; color: var(--soft); display: flex; flex-direction: column; align-items: center; gap: 1px; }
#tabs .icon { font-size: 18px; line-height: 1.2; }
#tabs button[aria-current="page"] { color: var(--accent); font-weight: 700; }

form.login { margin-top: 18vh; }
.logo { font: 700 40px/1.2 var(--serif); letter-spacing: .2em; margin: 0 0 6px; }
form.login input { width: 100%; font: inherit; padding: 14px 16px; border-radius: var(--radius); border: 1.5px solid var(--line); background: var(--card); color: var(--ink); margin: 14px 0; }
.error { color: var(--bad); min-height: 1.75em; }
@media (min-width: 760px) {
  body { font-size: 17.5px; }
  main { padding-top: 36px; }
  .tiles { grid-template-columns: 1fr 1fr; }
}
.practice { display: flex; align-items: center; justify-content: space-between; gap: 12px; background: var(--card); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 12px 16px; margin: 6px 0 14px; }
.practice > div { display: flex; flex-direction: column; gap: 2px; }
.practice small { color: var(--soft); }
.practice .pill { flex: none; }
.nobr { white-space: nowrap; }
.option .again { display: block; margin-top: 4px; color: var(--accent); font-size: 13px; font-weight: 700; }
/* mistakes */
button.stat { width: 100%; background: none; border-width: 0 0 1px; border-style: solid; border-color: var(--line); color: inherit; font: inherit; text-align: left; cursor: pointer; }
.mistake-node { margin: 16px 0 6px; }
.mistake { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); margin: 0 0 10px; padding: 0 16px; }
.mistake summary { padding: 14px 0; cursor: pointer; font-weight: 600; }
.mistake summary .times { color: var(--bad); font-weight: 700; }
.mistake[open] { padding-bottom: 4px; }
/* the knowledge map: a pyramid, foundation at the bottom */
.viewtoggle { margin: 18px 0 4px; }
.map { position: relative; margin: 8px 0 12px; }
.map .links { position: absolute; inset: 0; pointer-events: none; overflow: visible; }
.map .links line { stroke-width: 2; }
.map .links line.down { stroke: var(--good); }
.map .links line.up { stroke: var(--accent); stroke-dasharray: 4 4; }
.layer { position: relative; padding: 10px 0 12px; border-top: 1px dashed var(--line); }
.layer:last-of-type { border-bottom: 2px solid var(--line); }
.layer .depth { display: block; color: var(--soft); font-size: 12.5px; letter-spacing: .1em; margin-bottom: 6px; }
.mapchips { display: flex; flex-wrap: wrap; justify-content: center; gap: 8px; }
.mapnode { position: relative; z-index: 1; border: 1.5px solid var(--line); background: var(--card); color: var(--ink); border-radius: 10px; padding: 6px 10px;
  font: inherit; font-size: 14px; line-height: 1.3; cursor: pointer; transition: opacity .15s; }
.mapnode.s-mastered { border-color: var(--good); background: var(--good); color: var(--card); }
.mapnode.s-skipped { border-color: var(--good); background: var(--good-wash); }
.mapnode.s-learning { border-color: var(--accent); background: var(--accent-wash, var(--wash)); }
.mapnode.s-due { border-color: var(--accent); border-width: 2.5px; font-weight: 700; }
.mapnode.s-locked { border-style: dashed; color: var(--soft); }
.mapnode.weak { box-shadow: 0 0 0 2.5px var(--bad); }
.map.focus .mapnode:not(.on):not(.below):not(.above) { opacity: .28; }
.mapnode.on { outline: 3px solid var(--ink); outline-offset: 2px; }
.mapcard { position: sticky; bottom: calc(72px + env(safe-area-inset-bottom)); z-index: 3; background: var(--card); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 12px 14px; margin: 8px 0; display: grid; gap: 4px; }
.mapcard .note { margin: 0; }
.mapcard .pill { justify-self: start; }
.legend .mapnode { cursor: default; font-size: 12px; padding: 3px 8px; margin: 0 6px 6px 0; display: inline-block; }
.mapcard[hidden] { display: none; }
.mapnode.below { outline: 2px solid var(--good); outline-offset: 2px; opacity: 1; }
.mapnode.above { outline: 2px dashed var(--accent); outline-offset: 2px; opacity: 1; }
.videos { margin: 0; padding-left: 20px; font-size: 14px; line-height: 1.6; }
.videos small { color: var(--soft); }
/* display settings */
.display { display: grid; gap: 10px; margin: 0 0 18px; }
.display > div { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.display .chips { gap: 6px; }