:root {
  --bg: #f6f4ef;
  --bg-2: #efece4;
  --card: #fffdf9;
  --ink: #1d2230;
  --ink-2: #4a5165;
  --ink-3: #7b8196;
  --line: #e2ded3;
  --line-2: #d3cec1;
  --accent: #2f5bd3;
  --accent-2: #264bb0;
  --accent-soft: #e6ecfb;
  --good: #1f8a5b;
  --good-soft: #e3f3ea;
  --bad: #c2413b;
  --bad-soft: #fbe9e7;
  --warn: #b7791f;
  --warn-soft: #fbf1dc;
  --m0: #eef0f5; --m1: #d6e0fb; --m2: #a9bff5; --m3: #6f93ec; --m4: #3a68df; --m5: #1f47b5;
  --shadow: 0 1px 2px rgba(29,34,48,.05), 0 6px 24px rgba(29,34,48,.06);
  --radius: 14px;
  --plot-grid: #e8e4da;
  --plot-axis: #6b7185;
  --plot-curve: #2f5bd3;
  --plot-asym: #c2413b;
  --plot-text: #4a5165;
  --serif: "Fraunces", "Iowan Old Style", Georgia, serif;
  --sans: "Inter", ui-sans-serif, system-ui, -apple-system, "Segoe UI", sans-serif;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #12141b; --bg-2: #181b24; --card: #1b1f2a; --ink: #e8eaf2; --ink-2: #b5bacb; --ink-3: #8a90a6;
    --line: #2a2f3d; --line-2: #363c4d; --accent: #7c9cff; --accent-2: #9bb3ff; --accent-soft: #232c49;
    --good: #4cc38a; --good-soft: #17301f; --bad: #ff7a70; --bad-soft: #3a1c1b; --warn: #e3b25a; --warn-soft: #33291a;
    --m0: #232733; --m1: #25335c; --m2: #2c4486; --m3: #3a5cb8; --m4: #5b80e6; --m5: #8fb0ff;
    --shadow: 0 1px 2px rgba(0,0,0,.3), 0 8px 28px rgba(0,0,0,.35);
    --plot-grid: #262b38; --plot-axis: #9aa1b8; --plot-curve: #8fb0ff; --plot-asym: #ff7a70; --plot-text: #b5bacb;
  }
}
:root[data-theme="dark"] {
  --bg: #12141b; --bg-2: #181b24; --card: #1b1f2a; --ink: #e8eaf2; --ink-2: #b5bacb; --ink-3: #8a90a6;
  --line: #2a2f3d; --line-2: #363c4d; --accent: #7c9cff; --accent-2: #9bb3ff; --accent-soft: #232c49;
  --good: #4cc38a; --good-soft: #17301f; --bad: #ff7a70; --bad-soft: #3a1c1b; --warn: #e3b25a; --warn-soft: #33291a;
  --m0: #232733; --m1: #25335c; --m2: #2c4486; --m3: #3a5cb8; --m4: #5b80e6; --m5: #8fb0ff;
  --shadow: 0 1px 2px rgba(0,0,0,.3), 0 8px 28px rgba(0,0,0,.35);
  --plot-grid: #262b38; --plot-axis: #9aa1b8; --plot-curve: #8fb0ff; --plot-asym: #ff7a70; --plot-text: #b5bacb;
}

* { box-sizing: border-box; }
html, body { margin: 0; background: var(--bg); color: var(--ink); font: 15px/1.55 var(--sans); -webkit-font-smoothing: antialiased; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
button { font: inherit; color: inherit; }
.katex { font-size: 1.06em; }
.katex-display { margin: .6em 0; overflow-x: auto; overflow-y: hidden; padding: 2px 0; }

/* ---------- layout ---------- */
.shell { display: grid; grid-template-columns: 232px 1fr; min-height: 100vh; }
.side { position: sticky; top: 0; height: 100vh; padding: 22px 14px; border-right: 1px solid var(--line); background: var(--bg); display: flex; flex-direction: column; gap: 4px; }
.brand { display: flex; align-items: center; gap: 10px; padding: 4px 10px 18px; font-family: var(--serif); font-size: 21px; font-weight: 600; letter-spacing: -.01em; }
.brand-mark { width: 30px; height: 30px; border-radius: 9px; background: linear-gradient(135deg, var(--accent), #8a5cf6); display: grid; place-items: center; color: white; font-size: 16px; font-weight: 700; font-family: var(--sans); }
.nav a { display: flex; align-items: center; gap: 11px; padding: 9px 12px; border-radius: 10px; color: var(--ink-2); font-weight: 500; }
.nav a svg { width: 18px; height: 18px; flex: none; opacity: .85; }
.nav a:hover { background: var(--bg-2); text-decoration: none; color: var(--ink); }
.nav a.on { background: var(--card); color: var(--ink); box-shadow: var(--shadow); }
.side-foot { margin-top: auto; padding: 10px 12px; font-size: 12px; color: var(--ink-3); }
.side-foot .xpbar { height: 6px; border-radius: 3px; background: var(--line); overflow: hidden; margin: 6px 0 4px; }
.side-foot .xpbar i { display: block; height: 100%; background: var(--accent); border-radius: 3px; }
main { padding: 30px clamp(16px, 4vw, 44px) 80px; max-width: 1180px; width: 100%; min-width: 0; box-sizing: border-box; }
.page-title { font-family: var(--serif); font-weight: 600; font-size: 30px; letter-spacing: -.015em; margin: 0 0 4px; }
.page-sub { color: var(--ink-3); margin: 0 0 24px; }

/* ---------- cards ---------- */
.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow); padding: 20px; }
.grid { display: grid; gap: 16px; }
.g2 { grid-template-columns: 1.4fr 1fr; }
.g4 { grid-template-columns: repeat(4, 1fr); }
.stat .k { color: var(--ink-3); font-size: 12.5px; font-weight: 500; text-transform: uppercase; letter-spacing: .06em; }
.stat .v { font-size: 28px; font-weight: 650; letter-spacing: -.02em; margin-top: 2px; font-variant-numeric: tabular-nums; }
.stat .s { color: var(--ink-3); font-size: 13px; }
h2.sec { font-size: 13px; text-transform: uppercase; letter-spacing: .08em; color: var(--ink-3); font-weight: 600; margin: 28px 0 10px; }

.hero { display: flex; gap: 22px; align-items: center; justify-content: space-between; background: linear-gradient(135deg, var(--card), var(--accent-soft)); }
.hero h3 { margin: 4px 0 6px; font-size: 22px; letter-spacing: -.01em; }
.hero .kicker { font-size: 12px; font-weight: 600; color: var(--accent); text-transform: uppercase; letter-spacing: .08em; }
.hero .why { color: var(--ink-2); font-size: 14px; }

.btn { display: inline-flex; align-items: center; gap: 8px; border: 1px solid var(--line-2); background: var(--card); padding: 9px 15px; border-radius: 10px; cursor: pointer; font-weight: 550; transition: transform .06s ease, background .15s; }
.btn:hover { background: var(--bg-2); }
.btn:active { transform: translateY(1px); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: white; }
.btn.primary:hover { background: var(--accent-2); }
.btn.big { padding: 13px 22px; font-size: 16px; border-radius: 12px; }
.btn.ghost { border-color: transparent; background: transparent; color: var(--ink-2); }
.btn.ghost:hover { background: var(--bg-2); }
.btn.sm { padding: 5px 10px; font-size: 13px; border-radius: 8px; }
.btn:disabled { opacity: .5; cursor: default; }
.row { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
.spacer { flex: 1; }
.muted { color: var(--ink-3); }
.chip { display: inline-flex; align-items: center; gap: 6px; padding: 2px 9px; border-radius: 999px; font-size: 12px; font-weight: 550; background: var(--bg-2); color: var(--ink-2); border: 1px solid var(--line); white-space: nowrap; }
.chip.good { background: var(--good-soft); color: var(--good); border-color: transparent; }
.chip.bad { background: var(--bad-soft); color: var(--bad); border-color: transparent; }
.chip.warn { background: var(--warn-soft); color: var(--warn); border-color: transparent; }
.chip.acc { background: var(--accent-soft); color: var(--accent); border-color: transparent; }
.dot { width: 9px; height: 9px; border-radius: 50%; display: inline-block; flex: none; }

/* ---------- lists ---------- */
.list { display: flex; flex-direction: column; }
.list .it { display: flex; gap: 12px; align-items: center; padding: 11px 4px; border-top: 1px solid var(--line); }
.list .it:first-child { border-top: 0; }
.list .it .t { font-weight: 550; }
.list .it .d { color: var(--ink-3); font-size: 13px; }
.tag-type { font-size: 11px; font-weight: 650; text-transform: uppercase; letter-spacing: .06em; padding: 3px 7px; border-radius: 6px; }
.tag-type.lesson { background: var(--accent-soft); color: var(--accent); }
.tag-type.review { background: var(--good-soft); color: var(--good); }
.tag-type.quiz { background: var(--warn-soft); color: var(--warn); }
.bar { height: 8px; border-radius: 4px; background: var(--bg-2); overflow: hidden; }
.bar i { display: block; height: 100%; background: var(--accent); border-radius: 4px; transition: width .4s ease; }
.chapter-row { display: grid; grid-template-columns: 34px 1fr 150px 64px; gap: 12px; align-items: center; padding: 9px 0; border-top: 1px solid var(--line); }
.chapter-row:first-child { border-top: 0; }
.chapter-row .n { font-family: var(--serif); font-weight: 600; color: var(--ink-3); font-size: 18px; }

.week { display: flex; gap: 8px; align-items: flex-end; height: 90px; }
.week .d { flex: 1; display: flex; flex-direction: column; align-items: center; gap: 5px; font-size: 11px; color: var(--ink-3); }
.week .d i { width: 100%; border-radius: 6px 6px 3px 3px; background: var(--m2); min-height: 3px; }
.week .d.today i { background: var(--accent); }

.ring { width: 76px; height: 76px; }

/* ---------- study ---------- */
.study { max-width: 820px; margin: 0 auto; }
.study-top { display: flex; align-items: center; gap: 14px; margin-bottom: 18px; }
.study-top .title { font-weight: 650; font-size: 17px; }
.study-top .sub { color: var(--ink-3); font-size: 13px; }
.progress { flex: 1; }
.pane { background: var(--card); border: 1px solid var(--line); border-radius: 18px; box-shadow: var(--shadow); padding: clamp(18px, 3vw, 30px); }
.pane + .pane { margin-top: 16px; }
.prompt { font-size: 17px; line-height: 1.65; }
.prompt p { margin: 0 0 .7em; }
.figure { display: flex; justify-content: center; margin: 14px 0 6px; }
.figure svg.fg { width: min(360px, 100%); height: auto; }
.parts { display: flex; flex-direction: column; gap: 14px; margin-top: 18px; }
.part label.lab { display: block; font-size: 13px; font-weight: 600; color: var(--ink-2); margin-bottom: 6px; }
.ans-wrap { display: flex; align-items: stretch; border: 1.5px solid var(--line-2); border-radius: 11px; background: var(--bg); overflow: hidden; transition: border-color .15s, box-shadow .15s; }
.ans-wrap:focus-within { border-color: var(--accent); box-shadow: 0 0 0 4px var(--accent-soft); }
.ans-wrap .prefix { padding: 11px 0 11px 13px; color: var(--ink-3); font-weight: 550; white-space: nowrap; }
.ans-wrap input { flex: 1; min-width: 0; border: 0; outline: 0; background: transparent; padding: 11px 13px; font: 16px/1.3 ui-monospace, "SF Mono", Menlo, monospace; color: var(--ink); }
.preview { min-height: 22px; font-size: 14px; color: var(--ink-2); margin-top: 6px; padding-left: 2px; }
.preview .err { color: var(--warn); font-size: 13px; }
.preview .lbl { color: var(--ink-3); font-size: 12px; margin-right: 6px; }
.formhint { font-size: 12.5px; color: var(--accent); margin-top: 4px; }
.choices { display: grid; gap: 10px; }
.choices.figs { grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); }
.choice { text-align: left; border: 1.5px solid var(--line-2); background: var(--bg); border-radius: 12px; padding: 12px 14px; cursor: pointer; display: flex; gap: 12px; align-items: flex-start; transition: border-color .12s, background .12s; }
.choice:hover { border-color: var(--accent); }
.choice.on { border-color: var(--accent); background: var(--accent-soft); box-shadow: 0 0 0 3px var(--accent-soft); }
.choice .letter { flex: none; width: 24px; height: 24px; border-radius: 7px; background: var(--bg-2); display: grid; place-items: center; font-size: 12px; font-weight: 700; color: var(--ink-2); }
.choice.on .letter { background: var(--accent); color: white; }
.choice .fig svg.fg { width: 100%; height: auto; }
.choice.fig-choice { flex-direction: column; align-items: stretch; }
.actions { display: flex; gap: 10px; align-items: center; margin-top: 22px; }
.kbd { font-size: 12px; color: var(--ink-3); }

.banner { display: flex; gap: 12px; align-items: center; padding: 14px 16px; border-radius: 12px; font-weight: 600; font-size: 16px; }
.banner.good { background: var(--good-soft); color: var(--good); }
.banner.bad { background: var(--bad-soft); color: var(--bad); }
.banner svg { width: 22px; height: 22px; flex: none; }
.pres { display: flex; flex-direction: column; gap: 8px; margin: 14px 0 4px; }
.pres .pr { display: grid; grid-template-columns: 22px 1fr; gap: 10px; padding: 10px 12px; border-radius: 10px; background: var(--bg); border: 1px solid var(--line); }
.pres .pr .ic { font-weight: 700; }
.pres .pr.good .ic { color: var(--good); }
.pres .pr.bad .ic { color: var(--bad); }
.mistake { margin-top: 6px; padding: 9px 12px; border-left: 3px solid var(--warn); background: var(--warn-soft); border-radius: 0 8px 8px 0; font-size: 14px; }
.solution { margin-top: 16px; }
.solution h4 { margin: 0 0 10px; font-size: 13px; text-transform: uppercase; letter-spacing: .08em; color: var(--ink-3); }
.steps { counter-reset: s; list-style: none; padding: 0; margin: 0; display: flex; flex-direction: column; gap: 8px; }
.steps li { counter-increment: s; display: grid; grid-template-columns: 28px 1fr; gap: 10px; align-items: baseline; }
.steps li::before { content: counter(s); width: 22px; height: 22px; border-radius: 50%; background: var(--accent-soft); color: var(--accent); font-size: 12px; font-weight: 700; display: grid; place-items: center; }
.explain { font-size: 16.5px; line-height: 1.7; }
.explain p { margin: 0 0 .8em; }
.intro-kicker { font-size: 12px; font-weight: 650; color: var(--accent); text-transform: uppercase; letter-spacing: .08em; }
.example { margin-top: 18px; border: 1px dashed var(--line-2); border-radius: 14px; padding: 18px; background: var(--bg); }
.example .ex-h { font-size: 12px; font-weight: 700; color: var(--ink-3); text-transform: uppercase; letter-spacing: .08em; margin-bottom: 8px; }
.answer-box { margin-top: 12px; padding: 10px 12px; background: var(--good-soft); border-radius: 10px; font-size: 15px; }
.summary-big { text-align: center; padding: 26px 10px; }
.summary-big .emoji { font-size: 44px; }
.summary-big h2 { font-family: var(--serif); font-size: 28px; margin: 8px 0 4px; }
.xp-pop { display: inline-block; font-weight: 750; color: var(--accent); font-size: 20px; margin-top: 6px; }
.video-link { display: inline-flex; gap: 6px; align-items: center; font-size: 13px; }

/* ---------- graph input ---------- */
.gi { border: 1.5px solid var(--line-2); border-radius: 14px; background: var(--bg); padding: 10px; }
.gi-tools { display: flex; gap: 6px; flex-wrap: wrap; margin-bottom: 8px; }
.gi-tools .btn.on { background: var(--accent); color: white; border-color: var(--accent); }
.gi svg { width: 100%; max-width: 420px; height: auto; display: block; margin: 0 auto; touch-action: none; cursor: crosshair; }
.gi-hint { font-size: 12.5px; color: var(--ink-3); margin-top: 6px; text-align: center; }

/* ---------- plots (problem figures) ---------- */
svg.fg .fg-grid { stroke: var(--plot-grid); stroke-width: 1; }
svg.fg .fg-axis { stroke: var(--plot-axis); stroke-width: 1.4; }
svg.fg .fg-axis-head { fill: var(--plot-axis); }
svg.fg .fg-axis-label { fill: var(--plot-text); font: italic 13px var(--serif); }
svg.fg .fg-tick { fill: var(--plot-text); font: 10.5px var(--sans); }
svg.fg .fg-curve { stroke: var(--plot-curve); stroke-width: 2.6; fill: none; stroke-linecap: round; stroke-linejoin: round; }
svg.fg .fg-arrowhead { fill: var(--plot-curve); }
svg.fg .fg-asym { stroke: var(--plot-asym); stroke-width: 1.6; stroke-dasharray: 6 5; }
svg.fg .fg-dot { fill: var(--plot-curve); stroke: var(--card); stroke-width: 1.2; }
svg.fg .fg-dot-open { fill: var(--card); stroke: var(--plot-curve); stroke-width: 2.2; }
svg.fg .fg-label { fill: var(--ink); font: 600 11.5px var(--sans); paint-order: stroke; stroke: var(--card); stroke-width: 3px; }
svg.fg .fg-asym-label { fill: var(--plot-asym); }
.gi .u-curve { stroke: var(--plot-curve); stroke-width: 2.6; fill: none; stroke-linecap: round; }
.gi .u-dot { fill: var(--plot-curve); }
.gi .u-dot-open { fill: var(--bg); stroke: var(--plot-curve); stroke-width: 2.4; }
.gi .u-asym { stroke: var(--plot-asym); stroke-width: 2; stroke-dasharray: 7 5; }
.gi .u-pending { fill: var(--warn); }
.gi .u-ghost { stroke: var(--warn); stroke-width: 2; stroke-dasharray: 4 4; fill: none; }

/* ---------- map ---------- */
.map-wrap { overflow: auto; background: var(--card); border: 1px solid var(--line); border-radius: 18px; box-shadow: var(--shadow); }
.map-wrap svg { display: block; }
.map-node rect { stroke: var(--line-2); stroke-width: 1; transition: opacity .15s; }
.map-node text { font: 500 10.5px var(--sans); fill: var(--ink); pointer-events: none; }
.map-node.dark text { fill: white; }
.map-node { cursor: pointer; }
.map-edge { fill: none; stroke: var(--line-2); stroke-width: 1; opacity: .55; transition: opacity .15s, stroke .15s; }
.map-edge.hi { stroke: var(--accent); opacity: 1; stroke-width: 1.6; }
.map-edge.enc { stroke: var(--good); stroke-dasharray: 3 3; }
.map-dim .map-node:not(.hi) { opacity: .28; }
.map-dim .map-edge:not(.hi) { opacity: .08; }
.map-col-title { font: 650 12px var(--sans); fill: var(--ink-3); text-transform: uppercase; letter-spacing: .08em; }
.legend { display: flex; gap: 14px; align-items: center; flex-wrap: wrap; font-size: 12.5px; color: var(--ink-2); margin: 0 0 12px; }
.legend .sw { width: 14px; height: 14px; border-radius: 4px; display: inline-block; border: 1px solid var(--line-2); vertical-align: -2px; margin-right: 5px; }
.tooltip { position: fixed; z-index: 50; pointer-events: none; background: var(--ink); color: var(--bg); padding: 8px 11px; border-radius: 9px; font-size: 12.5px; max-width: 280px; box-shadow: var(--shadow); }

/* ---------- topics ---------- */
.search { width: 100%; padding: 11px 14px; border-radius: 11px; border: 1.5px solid var(--line-2); background: var(--card); font: inherit; color: var(--ink); outline: none; }
.search:focus { border-color: var(--accent); box-shadow: 0 0 0 4px var(--accent-soft); }
.topic-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(290px, 1fr)); gap: 10px; }
.topic-card { display: flex; gap: 12px; align-items: center; padding: 12px 14px; border-radius: 12px; background: var(--card); border: 1px solid var(--line); cursor: pointer; transition: border-color .12s, transform .08s; }
.topic-card:hover { border-color: var(--accent); }
.topic-card .sq { width: 34px; height: 34px; border-radius: 9px; flex: none; display: grid; place-items: center; font-size: 11px; font-weight: 700; color: var(--ink-2); border: 1px solid var(--line-2); }
.topic-card .t { font-weight: 560; font-size: 14px; line-height: 1.3; }
.topic-card .d { font-size: 12px; color: var(--ink-3); }
.kp { padding: 14px 0; border-top: 1px solid var(--line); }
.kp:first-child { border-top: 0; }
.kp h4 { margin: 0 0 6px; font-size: 15px; }
.weights .w { display: grid; grid-template-columns: 1fr 90px 38px; gap: 10px; align-items: center; padding: 5px 0; font-size: 13.5px; }
.explore-controls { display: grid; grid-template-columns: 1fr 1fr auto; gap: 10px; align-items: end; }
select { font: inherit; color: var(--ink); background: var(--card); border: 1.5px solid var(--line-2); border-radius: 10px; padding: 9px 11px; width: 100%; }
.field label { display: block; font-size: 12.5px; font-weight: 600; color: var(--ink-3); margin-bottom: 5px; }
.toast { position: fixed; bottom: 22px; left: 50%; transform: translateX(-50%); background: var(--ink); color: var(--bg); padding: 10px 16px; border-radius: 10px; font-size: 14px; z-index: 60; box-shadow: var(--shadow); }
.empty { text-align: center; padding: 50px 20px; color: var(--ink-3); }
.check-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 4px 16px; max-height: 360px; overflow: auto; padding: 4px; }
.check-grid label { display: flex; gap: 8px; align-items: center; font-size: 13.5px; padding: 3px 0; }
details summary { cursor: pointer; font-weight: 600; }

/* ---------- responsive ---------- */
@media (max-width: 900px) {
  .shell { grid-template-columns: 1fr; }
  .side { position: fixed; bottom: 0; top: auto; height: auto; width: 100%; flex-direction: row; padding: 6px; border-right: 0; border-top: 1px solid var(--line); z-index: 40; background: var(--card); }
  .brand, .side-foot { display: none; }
  .nav { display: flex; width: 100%; justify-content: space-around; }
  .nav a { flex-direction: column; gap: 2px; font-size: 11px; padding: 6px 8px; }
  .nav a.on { box-shadow: none; background: var(--accent-soft); }
  main { padding: 20px 16px 90px; }
  .g2, .g4 { grid-template-columns: 1fr 1fr; }
  .g2 { grid-template-columns: 1fr; }
  .hero { flex-direction: column; align-items: flex-start; }
  .chapter-row { grid-template-columns: 28px 1fr 70px; }
  .chapter-row .pct { display: none; }
  .explore-controls { grid-template-columns: 1fr; }
}
.steps li p, .pres p, .answer-box p { margin: 0; }
.steps li p + p { margin-top: .4em; }

/* ---------- accounts ---------- */
body.auth-mode .side { display: none; }
body.auth-mode .shell { display: block; }
.auth { min-height: 100vh; display: grid; place-items: center; padding: 24px 16px; }
.auth-card { width: min(420px, 100%); padding: 28px 28px 22px; }
.auth-brand { padding: 0 0 12px; }
.auth-title { font-family: var(--serif); font-size: 26px; margin: 4px 0 16px; font-weight: 600; }
.auth-tabs { display: grid; grid-template-columns: 1fr 1fr; background: var(--bg-2); border-radius: 10px; padding: 3px; margin-bottom: 16px; }
.auth-tabs button { border: 0; background: transparent; padding: 8px; border-radius: 8px; font: inherit; font-weight: 600; color: var(--ink-3); cursor: pointer; }
.auth-tabs button.on { background: var(--card); color: var(--ink); box-shadow: var(--shadow); }
.auth-form { display: flex; flex-direction: column; gap: 12px; }
.auth-form p { margin: 0; font-size: 14px; }
input[type=email], input[type=password], input[type=text], .acct input, .auth-form input { font: inherit; color: var(--ink); background: var(--card); border: 1.5px solid var(--line-2); border-radius: 10px; padding: 10px 12px; width: 100%; box-sizing: border-box; }
.auth-form input:focus, .acct input:focus { outline: none; border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }
.auth-go { width: 100%; justify-content: center; margin-top: 4px; }
.auth-hint { font-size: 12.5px; color: var(--ink-3); margin-top: -4px; }
.auth-msg { min-height: 20px; margin-top: 12px; font-size: 14px; }
.auth-msg.bad { color: var(--bad); }
.auth-msg.good { color: var(--good); }
.auth-links { margin-top: 6px; font-size: 14px; }
.auth-links a { color: var(--accent); }
.avatar { width: 32px; height: 32px; border-radius: 50%; background: var(--accent-soft); color: var(--accent); display: grid; place-items: center; font-weight: 700; flex: none; }
.side-user { display: flex; align-items: center; gap: 10px; padding: 10px; margin: auto 0 0; border-top: 1px solid var(--line); }
.side-user + .side-foot { margin-top: 0; }
.side-user .who { flex: 1; min-width: 0; display: flex; flex-direction: column; font-size: 13px; line-height: 1.3; }
.side-user .who b, .side-user .who span { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.side-user .who span { color: var(--ink-3); font-size: 12px; }
.acct-who { display: flex; gap: 12px; align-items: center; }
.acct .row input { flex: 1; min-width: 0; }
.acct-msg.good { color: var(--good); } .acct-msg.bad { color: var(--bad); }
.acct-danger { margin-top: 18px; }
.acct-danger summary { color: var(--bad); }
.linkish { background: none; border: 0; padding: 0; color: var(--accent); cursor: pointer; font: inherit; }
.linkish:hover { text-decoration: underline; }

/* ---------- notifications ---------- */
.bell-wrap { position: absolute; top: 18px; right: 12px; z-index: 30; }
.bell { position: relative; width: 34px; height: 34px; border-radius: 10px; border: 1px solid transparent; background: transparent; color: var(--ink-2); cursor: pointer; display: grid; place-items: center; }
.bell:hover, .bell[aria-expanded=true] { background: var(--bg-2); border-color: var(--line); }
.bell svg { width: 19px; height: 19px; }
.bell-n { position: absolute; top: 2px; right: 1px; min-width: 16px; height: 16px; padding: 0 4px; border-radius: 8px; background: var(--bad); color: #fff; font-size: 10.5px; font-weight: 700; line-height: 16px; box-sizing: border-box; }
.bell-panel { position: absolute; left: 0; top: 40px; width: 340px; max-height: 70vh; overflow: auto; background: var(--card); border: 1px solid var(--line); border-radius: 12px; box-shadow: 0 12px 40px rgba(0,0,0,.25); }
.bell-h { display: flex; justify-content: space-between; align-items: center; padding: 12px 14px; border-bottom: 1px solid var(--line); position: sticky; top: 0; background: var(--card); }
.bell-h .linkish { font-size: 13px; }
.bell-list { list-style: none; margin: 0; padding: 0; }
.bell-list li { padding: 11px 14px 11px 24px; border-bottom: 1px solid var(--line); cursor: pointer; position: relative; }
.bell-list li:hover, .bell-list li:focus { background: var(--bg-2); outline: none; }
.bell-list li.unread::before { content: ""; position: absolute; left: 10px; top: 17px; width: 7px; height: 7px; border-radius: 50%; background: var(--accent); }
.bell-t { font-weight: 600; font-size: 14px; }
.bell-list li:not(.unread) .bell-t { font-weight: 500; color: var(--ink-2); }
.bell-b { font-size: 13px; color: var(--ink-2); margin-top: 2px; }
.bell-m { font-size: 11.5px; color: var(--ink-3); margin-top: 4px; }
.bell-empty { padding: 26px 18px; text-align: center; color: var(--ink-3); font-size: 14px; }
.bell-f { padding: 10px 14px; font-size: 13px; }
.bell-f a { color: var(--accent); }
.rem .tog, .tog { display: grid; grid-template-columns: 18px 1fr; gap: 8px; align-items: start; font-size: 14px; padding: 5px 0; line-height: 1.4; }
.tog input { margin: 3px 0 0; }
.rem-hours { margin-top: 10px; display: grid; grid-template-columns: repeat(auto-fit, minmax(118px, 1fr)); gap: 10px; }
.g3 { grid-template-columns: repeat(3, 1fr); gap: 10px; }
.rem-tz { font-size: 13px; margin-top: 8px; }
.rem-kinds { display: grid; grid-template-columns: repeat(auto-fit, minmax(170px, 1fr)); gap: 0 12px; }
@media (max-width: 900px) {
  .bell-wrap { position: fixed; top: 10px; right: 10px; }
  .bell { background: var(--card); border-color: var(--line); }
  .bell-panel { left: auto; right: 0; width: min(340px, calc(100vw - 20px)); }
  .side-user { display: none; }
  .rem-kinds, .g3 { grid-template-columns: 1fr; }
}
body.auth-mode main { padding: 0; }
.auth { box-sizing: border-box; }

/* ---------- study flow, home, onboarding ---------- */
.study-top .title { flex: 1; min-width: 0; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.study-top .progress { flex: none; width: min(220px, 30vw); }
.kp-title { margin: 0 0 12px; font-size: 22px; }
.err { color: var(--bad); font-size: 14px; }
.pr.bad > div > div + div { margin-top: 4px; }
.graph-answer { margin-top: 10px; }
.graph-answer .muted { font-size: 13px; margin-bottom: 4px; }
.home { max-width: 820px; }
.home .hero { margin-top: 18px; }
.today { display: flex; gap: 34px; align-items: center; margin-top: 16px; padding: 16px 20px; flex-wrap: wrap; }
.today > div { display: flex; flex-direction: column; }
.today b { font-size: 18px; }
.today span { color: var(--ink-3); font-size: 13px; }
.today .today-goal { flex-direction: row; align-items: center; gap: 12px; }
.today .ring { width: 48px; height: 48px; }
.dev-note { margin-top: 10px; font-size: 13px; }
.onboard .grid { margin-top: 18px; }
.choice-card { display: flex; flex-direction: column; justify-content: flex-start; align-items: flex-start; text-align: left; cursor: pointer; font: inherit; color: inherit; border: 1.5px solid var(--line); transition: border-color .12s, transform .06s; }
.choice-card:hover, .choice-card:focus-visible { border-color: var(--accent); outline: none; }
.choice-card:active { transform: translateY(1px); }
.choice-card h3 { margin: 0 0 6px; font-size: 19px; }
.choice-card p { margin: 0; color: var(--ink-2); }
.crumb { font-size: 13px; color: var(--ink-3); margin-bottom: 6px; }
.crumb a { color: inherit; }
.lp-row { justify-content: space-between; padding: 5px 0; flex-wrap: nowrap; }
.link-row { padding: 3px 0; }
.check-head { grid-column: 1 / -1; font-weight: 650; font-size: 12.5px; color: var(--ink-3); margin-top: 6px; }
.check-grid { margin-top: 10px; }
.res { font-weight: 600; }
.res.good { color: var(--good); } .res.bad { color: var(--bad); } .res.warn { color: var(--warn); }
a.it, a.topic-card { color: inherit; text-decoration: none; }
.topic-card .t { flex: 1; min-width: 0; }
.side-user .who { display: block; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; font-size: 13.5px; font-weight: 550; }
.pres .pr.solo { display: block; }
.pres .pr.solo .muted { margin-right: 6px; }
.banner.info { background: var(--accent-soft); color: var(--accent); }
.today .today-goal > div { display: flex; flex-direction: column; }

@media (max-width: 900px) { .study-top { padding-right: 50px; } .page-title { padding-right: 50px; } }

.none-opt { display: flex; align-items: center; gap: 8px; margin-top: 8px; color: var(--ink-2); cursor: pointer; }
.ans-wrap.off input { opacity: .45; }
.answer-box > div { margin-top: 10px; }
.answer-box > div:empty { display: none; }
.answer-box .gr-thumb { display: block; width: max-content; max-width: 100%; }

/* ------------------------------------------------------------------ Learn (learn.js) */
.learn-head { margin-bottom: 18px; display: grid; gap: 10px; }
.lh-top { display: flex; align-items: center; gap: 10px; }
.lh-top .page-title { margin: 0; }
.lh-line { color: var(--ink-2); font-size: 15px; }
.lh-today { font-size: 13px; }
.lh-today:empty { display: none; }
.lh-settings { border-top: 1px solid var(--line); padding-top: 14px; display: grid; gap: 14px; }
.lh-settings[hidden] { display: none; }
.seg-field { border: 0; margin: 0; padding: 0; min-width: 0; }
.seg-field legend { font-weight: 600; font-size: 14px; margin-bottom: 6px; padding: 0; }
.seg { display: inline-flex; flex-wrap: wrap; border: 1px solid var(--line-2); border-radius: 10px; overflow: hidden; background: var(--card); }
.seg-opt { position: relative; }
.seg-opt input { position: absolute; opacity: 0; inset: 0; margin: 0; cursor: pointer; }
.seg-opt span { display: block; padding: 7px 14px; font-size: 14px; font-weight: 550; color: var(--ink-2); border-right: 1px solid var(--line); }
.seg-opt:last-child span { border-right: 0; }
.seg-opt input:checked + span { background: var(--accent); color: #fff; }
.seg-opt input:focus-visible + span { outline: 2px solid var(--accent); outline-offset: -3px; }
.seg-field .help { margin: 6px 0 0; font-size: 13px; }
.check { display: flex; gap: 8px; align-items: center; font-size: 14px; }
.feed { display: grid; gap: 16px; }
.learn-card.past { opacity: .72; }
.learn-card .kicker { font-size: 12px; font-weight: 600; color: var(--accent); text-transform: uppercase; letter-spacing: .08em; }
.learn-card .from { font-size: 13px; margin-top: 12px; }
.learn-card.teach .from { margin: -4px 0 12px; }
.pane.fb.in-card { border: 0; box-shadow: none; padding: 18px 0 0; margin-top: 18px; border-top: 1px solid var(--line); border-radius: 0; }
.event { margin-top: 10px; padding: 9px 12px; border-radius: 10px; font-size: 14px; font-weight: 550; }
.event.good { background: var(--good-soft); color: var(--good); }
.event.warn { background: var(--warn-soft); color: var(--warn); }
.event.acc { background: var(--accent-soft); color: var(--accent); }
.event .xp { font-weight: 700; margin-left: 6px; }
.side-task { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-top: 14px; padding: 14px 18px; }