:root {
  color-scheme: light dark;
  --paper: #f7f5ef;
  --card: #ffffff;
  --ink: #1d2433;
  --muted: #5d6474;
  --line: #e0dcd0;
  --accent: #2f46c4;
  --accent-ink: #ffffff;
  --accent-soft: #e6e9fb;
  --good: #14693f;
  --good-soft: #dff3e7;
  --bad: #a3271c;
  --bad-soft: #fbe6e2;
  --hint: #6e4c00;
  --hint-soft: #fbf0d0;
  --key: #ffffff;
  --key-op: #e9e6dc;
  --math: ui-serif, "New York", Georgia, "Times New Roman", serif;
  --sans: ui-rounded, -apple-system, BlinkMacSystemFont, "SF Pro Rounded", "Segoe UI", system-ui, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #14161c;
    --card: #1f222b;
    --ink: #eef0f5;
    --muted: #a5abb9;
    --line: #333744;
    --accent: #8d9ffa;
    --accent-ink: #11142a;
    --accent-soft: #272d52;
    --good: #6fd79f;
    --good-soft: #17352a;
    --bad: #ff9c8f;
    --bad-soft: #43221e;
    --hint: #f0cd7a;
    --hint-soft: #3a2f13;
    --key: #2a2e39;
    --key-op: #383d4b;
  }
}

:root[data-theme="dark"] {
  --paper: #14161c;
  --card: #1f222b;
  --ink: #eef0f5;
  --muted: #a5abb9;
  --line: #333744;
  --accent: #8d9ffa;
  --accent-ink: #11142a;
  --accent-soft: #272d52;
  --good: #6fd79f;
  --good-soft: #17352a;
  --bad: #ff9c8f;
  --bad-soft: #43221e;
  --hint: #f0cd7a;
  --hint-soft: #3a2f13;
  --key: #2a2e39;
  --key-op: #383d4b;
  color-scheme: dark;
}

:root[data-theme="light"] { color-scheme: light; }

* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; }

html, body {
  margin: 0;
  height: 100%;
  background: var(--paper);
  color: var(--ink);
  font: 17px/1.45 var(--sans);
  -webkit-text-size-adjust: 100%;
  overscroll-behavior: none;
}

button {
  font: inherit;
  color: inherit;
  background: none;
  border: 0;
  padding: 0;
  cursor: pointer;
  touch-action: manipulation;
}

button:focus-visible, textarea:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 2px;
}

h1, h2, h3, p, dl, dd, ol { margin: 0; padding: 0; }

#app { height: 100%; }

.screen {
  height: 100dvh;
  display: flex;
  flex-direction: column;
  max-width: 560px;
  margin: 0 auto;
  padding-top: env(safe-area-inset-top);
}

.scroll {
  flex: 1;
  min-height: 0;
  overflow-y: auto;
  -webkit-overflow-scrolling: touch;
  padding: 12px 16px calc(24px + env(safe-area-inset-bottom));
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.scroll > * { flex-shrink: 0; }

/* ---------- Top bar ---------- */

.bar {
  display: grid;
  grid-template-columns: 56px 1fr 56px;
  align-items: center;
  min-height: 48px;
  padding: 0 4px;
}

.bar-title {
  font-size: 17px;
  font-weight: 650;
  text-align: center;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.bar-right { text-align: right; padding-right: 10px; }
.count { font-size: 14px; color: var(--muted); white-space: nowrap; }

.icon-btn {
  width: 44px;
  height: 44px;
  display: grid;
  place-items: center;
  border-radius: 12px;
  color: var(--accent);
}

.meter { height: 4px; background: var(--line); flex-shrink: 0; }
.meter span { display: block; height: 100%; background: var(--accent); transition: width .25s ease; }

.pinned {
  flex-shrink: 0;
  text-align: center;
  font: 500 17px/1.3 var(--math);
  padding: 7px 12px;
  background: var(--card);
  border-bottom: 1px solid var(--line);
}

/* ---------- Home ---------- */

.home { padding-top: 22px; }
.eyebrow { color: var(--muted); font-size: 15px; font-weight: 600; }
.title { font-size: 34px; line-height: 1.1; font-weight: 750; letter-spacing: -.01em; margin-top: 4px; }

.home-head { display: flex; justify-content: space-between; align-items: flex-start; gap: 12px; }

.theme-toggle {
  flex-shrink: 0;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  min-height: 44px;
  padding: 0 12px;
  border: 1.5px solid var(--line);
  border-radius: 999px;
  font-size: 14px;
  font-weight: 600;
  color: var(--accent);
}

.theme-toggle:active { background: var(--accent-soft); }

.hero {
  display: flex;
  flex-direction: column;
  gap: 3px;
  width: 100%;
  text-align: left;
  background: var(--accent);
  color: var(--accent-ink);
  border-radius: 20px;
  padding: 18px 20px 20px;
  margin-top: 4px;
}

.hero-label { font-size: 14px; font-weight: 650; opacity: .85; }
.hero-title { font-size: 25px; font-weight: 750; line-height: 1.2; }
.hero-note { font-size: 15px; opacity: .92; }

.section { font-size: 19px; font-weight: 700; margin-top: 10px; }

.list {
  display: flex;
  flex-direction: column;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
  overflow: hidden;
}

.list-gap { margin-top: 2px; }

.skill-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  width: 100%;
  min-height: 64px;
  padding: 11px 16px;
  text-align: left;
}

.skill-row + .skill-row { border-top: 1px solid var(--line); }
.skill-row:active { background: var(--accent-soft); }
.skill-text { display: flex; flex-direction: column; min-width: 0; }
.skill-name { font-weight: 650; }
.skill-blurb { color: var(--muted); font-size: 14.5px; line-height: 1.3; }
.chevron { color: var(--muted); font-size: 24px; line-height: 1; }

.pips { display: inline-flex; gap: 5px; flex-shrink: 0; }
.pip { width: 11px; height: 11px; border-radius: 50%; border: 2px solid var(--line); }
.pip.done { background: var(--good); border-color: var(--good); }
.pip.now { border-color: var(--accent); background: var(--accent-soft); }

.badge {
  flex-shrink: 0;
  font-size: 13px;
  font-weight: 700;
  color: var(--good);
  background: var(--good-soft);
  border-radius: 999px;
  padding: 3px 10px;
}

.text-btn {
  align-self: center;
  color: var(--accent);
  font-size: 15px;
  font-weight: 600;
  min-height: 44px;
  padding: 0 12px;
}

.text-btn.danger { color: var(--bad); }

/* ---------- Problem and steps ---------- */

.practice { padding-bottom: 20px; }

.segs {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  background: var(--line);
  border-radius: 11px;
  padding: 3px;
}

.seg {
  min-height: 36px;
  font-size: 14px;
  font-weight: 600;
  color: var(--muted);
  border-radius: 9px;
}

.seg.on { background: var(--card); color: var(--ink); box-shadow: 0 1px 2px rgb(0 0 0 / .14); }

.problem {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 14px 16px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.eq-block {
  font: 500 20px/1.3 var(--math);
  text-align: center;
  padding: 2px 0;
}

.question { font-weight: 650; }

.work { list-style: none; display: flex; flex-direction: column; gap: 10px; padding: 0 4px; }
.work li { display: flex; flex-direction: column; gap: 1px; border-left: 3px solid var(--good); padding-left: 12px; }
.work-line { font: 500 17px/1.35 var(--math); overflow-wrap: anywhere; }
.work-why { color: var(--muted); font-size: 14.5px; line-height: 1.35; }
.shown-tag { color: var(--hint); font-weight: 700; }

.step {
  background: var(--card);
  border: 2px solid var(--accent);
  border-radius: 16px;
  padding: 14px 16px;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.step-prompt { font-weight: 500; overflow-wrap: anywhere; }

.entry-row { display: flex; align-items: center; gap: 8px; min-width: 0; }
.entry-label { font: 500 19px/1 var(--math); white-space: nowrap; }

.entry {
  flex: 1;
  min-width: 0;
  min-height: 46px;
  display: flex;
  align-items: center;
  padding: 6px 12px;
  border: 1.5px solid var(--line);
  border-radius: 11px;
  background: var(--paper);
  font: 500 20px/1.25 var(--math);
  overflow-wrap: anywhere;
  word-break: break-all;
}

.caret { display: inline-block; width: 2px; height: 22px; background: var(--accent); animation: blink 1.1s steps(2, start) infinite; }
@keyframes blink { to { visibility: hidden; } }

.preview { color: var(--muted); font-size: 15px; min-height: 0; text-align: right; }
.preview:empty { display: none; }

.feedback {
  background: var(--bad-soft);
  color: var(--bad);
  border-radius: 11px;
  padding: 10px 12px;
  font-size: 15.5px;
  font-weight: 500;
}

.hint {
  background: var(--hint-soft);
  color: var(--hint);
  border-radius: 11px;
  padding: 10px 12px;
  font-size: 15.5px;
}

.helpers { display: flex; flex-wrap: wrap; gap: 8px; }
.helpers:not(:has(button)) { display: none; }

.ghost {
  min-height: 42px;
  padding: 0 14px;
  border: 1.5px solid var(--line);
  border-radius: 11px;
  font-size: 15px;
  font-weight: 600;
  color: var(--accent);
}

.ghost:active { background: var(--accent-soft); }
.wide { width: 100%; }

.primary {
  min-height: 50px;
  padding: 0 18px;
  border-radius: 13px;
  background: var(--accent);
  color: var(--accent-ink);
  font-weight: 700;
}

.primary:active { filter: brightness(.9); }

.choices { display: flex; flex-direction: column; gap: 8px; }

.choice {
  width: 100%;
  min-height: 50px;
  padding: 10px 14px;
  text-align: left;
  background: var(--card);
  border: 1.5px solid var(--line);
  border-radius: 12px;
  overflow-wrap: anywhere;
}

.step .choice { background: var(--paper); }
.choice:active:not(:disabled) { border-color: var(--accent); background: var(--accent-soft); }
.choice:disabled { cursor: default; }
.choice.out { opacity: .5; }
.step .choice.out { text-decoration: line-through; }
.choice.right { border-color: var(--good); background: var(--good-soft); color: var(--good); font-weight: 700; }
.choice.wrong { border-color: var(--bad); background: var(--bad-soft); color: var(--bad); font-weight: 700; }

/* ---------- Keypad ---------- */

.keypad {
  flex-shrink: 0;
  background: var(--paper);
  border-top: 1px solid var(--line);
  padding: 8px 10px calc(8px + env(safe-area-inset-bottom));
  display: flex;
  flex-direction: column;
  gap: 7px;
}

.keys { display: grid; grid-template-columns: repeat(5, 1fr); gap: 6px; }

.key {
  height: 43px;
  border-radius: 10px;
  background: var(--key);
  font-size: 20px;
  font-weight: 500;
  box-shadow: 0 1px 0 var(--line);
  user-select: none;
  -webkit-user-select: none;
}

.key.op { background: var(--key-op); }
.key:active { background: var(--accent-soft); }

@media (max-height: 700px) {
  .key { height: 37px; font-size: 18px; }
  .keypad .primary { min-height: 42px; }
}

/* ---------- Finished ---------- */

.done { display: flex; flex-direction: column; gap: 10px; }
.done-label { color: var(--muted); font-size: 14px; font-weight: 650; text-align: center; margin-top: 6px; }
.done-answer { font: 600 34px/1.1 var(--math); text-align: center; margin-top: -8px; }
.sanity { font-size: 15.5px; color: var(--muted); }

.level-up {
  background: var(--good-soft);
  color: var(--good);
  border-radius: 11px;
  padding: 10px 12px;
  font-size: 15.5px;
  font-weight: 600;
}

/* ---------- Graph ---------- */

.graph {
  display: block;
  width: 100%;
  height: auto;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
}

.g-axis { stroke: var(--muted); stroke-width: 1.2; }
.g-curve { fill: none; stroke: var(--accent); stroke-width: 3; stroke-linecap: round; stroke-linejoin: round; }
.g-guide { stroke: var(--muted); stroke-width: 1.2; stroke-dasharray: 4 4; }
.g-dot { fill: var(--accent); stroke: var(--card); stroke-width: 2; }
.g-dot-soft { fill: var(--card); stroke: var(--accent); stroke-width: 2; }
.g-axis-label { font: 500 11px var(--sans); fill: var(--muted); }
.g-tick { font: 500 12px var(--sans); fill: var(--muted); }
.g-value { font: 700 13px var(--sans); fill: var(--ink); }

/* ---------- Lesson ---------- */

.lead { font-size: 18px; }

.meanings { display: flex; flex-direction: column; gap: 8px; }
.meanings > div { display: grid; grid-template-columns: 46px 1fr; gap: 10px; align-items: baseline; }
.meanings dt { font: 600 19px var(--math); text-align: right; }

.q-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 14px 16px;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.q-card h3, .callout h3 { font-size: 17px; font-weight: 700; }
.formula { font: 500 18px/1.3 var(--math); color: var(--accent); overflow-wrap: anywhere; }
.calc { font: 400 16px/1.35 var(--math); overflow-wrap: anywhere; }

.callout {
  background: var(--hint-soft);
  color: var(--hint);
  border-radius: 16px;
  padding: 14px 16px;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.run { gap: 12px; }
.run-title { font-size: 23px; line-height: 1.2; font-weight: 750; }
.lesson-eq { display: block; text-align: center; font: 500 19px/1.45 var(--math); padding: 8px 0 6px; overflow-wrap: anywhere; }

mark {
  background: var(--hint-soft);
  color: var(--hint);
  border-radius: 5px;
  padding: 0 3px;
  font-weight: 700;
}

.term.on {
  background: var(--hint-soft);
  color: var(--hint);
  border-radius: 5px;
  padding: 1px 4px;
  font-weight: 700;
}

.teach { color: var(--muted); font-size: 15.5px; line-height: 1.4; }
.tracker { font: 500 17px/1.4 var(--math); text-align: center; padding: 8px 6px; border-radius: 10px; background: var(--paper); overflow-wrap: anywhere; }

.task {
  background: var(--accent-soft);
  border-radius: 11px;
  padding: 10px 12px;
  font-weight: 650;
}

.task.met { background: var(--good-soft); color: var(--good); }
.readout { font: 500 16px/1.35 var(--math); text-align: center; min-height: 44px; overflow-wrap: anywhere; }

.slider-row { display: flex; align-items: center; gap: 12px; }
.slider-label { font: 600 17px/1 var(--math); white-space: nowrap; min-width: 62px; }
.slider-row input[type=range] { flex: 1; min-width: 0; height: 44px; accent-color: var(--accent); }

.after {
  background: var(--good-soft);
  color: var(--good);
  border-radius: 11px;
  padding: 10px 12px;
  font-size: 15.5px;
}

.after:empty { display: none; }

.run-nav {
  flex-shrink: 0;
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 8px;
  padding: 8px 12px calc(10px + env(safe-area-inset-bottom));
  border-top: 1px solid var(--line);
  background: var(--paper);
}

.run-nav.solo { grid-template-columns: 1fr; }
.run-nav .ghost { min-height: 50px; }
.primary:disabled { opacity: .4; cursor: default; }

.summary { display: flex; flex-direction: column; gap: 8px; padding-left: 20px; list-style: disc; }

.skill-card { padding: 12px 16px 14px; display: flex; flex-direction: column; gap: 10px; }
.skill-card + .skill-card { border-top: 1px solid var(--line); }
.skill-head { display: flex; justify-content: space-between; align-items: center; gap: 12px; }
.skill-actions { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; }
.skill-actions .ghost { min-height: 42px; }
.ghost.finished { color: var(--good); }

.g-grid { stroke: var(--line); stroke-width: 1; }
.g-curve-ghost { fill: none; stroke: var(--accent); stroke-width: 2.5; stroke-dasharray: 5 5; opacity: .75; }
.g-ball { fill: #e2851a; stroke: var(--card); stroke-width: 2; }

/* ---------- Backup ---------- */

.field-label { font-weight: 650; margin-top: 8px; margin-bottom: -8px; }

textarea {
  width: 100%;
  padding: 10px 12px;
  border: 1.5px solid var(--line);
  border-radius: 11px;
  background: var(--card);
  color: var(--ink);
  font: 16px/1.35 ui-monospace, Menlo, monospace;
  resize: none;
  word-break: break-all;
}

@media (prefers-reduced-motion: reduce) {
  * { animation: none !important; transition: none !important; }
}