:root {
  --bg: #f6f6f3;
  --surface: #ffffff;
  --surface-2: #efefea;
  --text: #1c1d1f;
  --muted: #6b6e73;
  --line: #e2e2dc;
  --accent: #0f766e;
  --accent-text: #ffffff;
  --accent-soft: #e0f2ef;
  --good: #15803d;
  --good-soft: #e7f6ec;
  --bad: #b91c1c;
  --bad-soft: #fcebea;
  --code-bg: #15171c;
  --code-text: #e6e6e6;
  --tok-kw: #ff7b8a;
  --tok-str: #a5e3b4;
  --tok-num: #f2c27b;
  --tok-fn: #8cc8ff;
  --tok-com: #7b818c;
  --radius: 12px;
  --shadow: 0 1px 2px rgb(0 0 0 / 0.04), 0 4px 16px rgb(0 0 0 / 0.04);
  --mono: ui-monospace, "Cascadia Code", "JetBrains Mono", Consolas, monospace;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #101113;
    --surface: #18191c;
    --surface-2: #222327;
    --text: #ececec;
    --muted: #9a9ca2;
    --line: #2c2d31;
    --accent: #2dd4bf;
    --accent-text: #06201d;
    --accent-soft: #123532;
    --good: #4ade80;
    --good-soft: #12301d;
    --bad: #f87171;
    --bad-soft: #3a1717;
    --code-bg: #0b0c0e;
    --shadow: none;
    color-scheme: dark;
  }
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.5 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  -webkit-font-smoothing: antialiased;
}

.app { max-width: 720px; margin: 0 auto; padding: 40px 16px 64px; }

h1, h2 { margin: 0; line-height: 1.25; }
h1 { font-size: 32px; letter-spacing: -0.02em; }
h2 { font-size: 15px; font-weight: 600; }

.eyebrow { margin: 0 0 6px; color: var(--accent); font-size: 13px; font-weight: 600; letter-spacing: 0.04em; text-transform: uppercase; }
.sub { margin: 8px 0 0; color: var(--muted); }
.head { margin-bottom: 28px; }

.block { margin-bottom: 28px; }
.block > h2, .block-head { margin-bottom: 10px; }
.block-head { display: flex; justify-content: space-between; align-items: baseline; }

code {
  font-family: var(--mono);
  font-size: 0.9em;
  background: var(--surface-2);
  padding: 1px 5px;
  border-radius: 5px;
}

/* Buttons */
.btn {
  appearance: none;
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--text);
  font: inherit;
  font-weight: 600;
  padding: 10px 18px;
  border-radius: 10px;
  cursor: pointer;
}
.btn:hover { border-color: var(--muted); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-text); }
.btn.primary:hover { filter: brightness(1.08); }
.btn.big { width: 100%; padding: 14px; font-size: 17px; }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }
.btn:focus-visible, .link:focus-visible, .opt:focus-within, .mode:focus-within, .topic:focus-within, .icon-btn:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.link { appearance: none; border: 0; background: none; color: var(--accent); font: inherit; font-size: 14px; cursor: pointer; padding: 0; }
.link:hover { text-decoration: underline; }
.link.muted { color: var(--muted); }

.icon-btn { appearance: none; border: 0; background: var(--surface-2); color: var(--text); width: 32px; height: 32px; border-radius: 8px; cursor: pointer; font-size: 14px; }

/* Topics */
.topics { list-style: none; margin: 0; padding: 0; display: grid; gap: 8px; }
.topic {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 14px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px 14px;
  box-shadow: var(--shadow);
}
.topic.off { opacity: 0.55; }
.topic input { width: 18px; height: 18px; accent-color: var(--accent); margin: 0; cursor: pointer; }
.topic label { cursor: pointer; min-width: 0; }
.topic-title { font-weight: 600; display: block; }
.topic-sub { color: var(--muted); font-size: 13px; display: flex; align-items: center; gap: 8px; }
.mastery { flex: 0 0 72px; height: 5px; border-radius: 3px; background: var(--surface-2); overflow: hidden; }
.mastery span { display: block; height: 100%; background: var(--accent); }

/* Modes */
.modes { display: grid; grid-template-columns: repeat(3, 1fr); gap: 8px; }
.mode { position: relative; cursor: pointer; }
.mode input { position: absolute; opacity: 0; }
.mode span {
  display: block;
  height: 100%;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px 14px;
}
.mode small { display: block; color: var(--muted); font-size: 13px; margin-top: 2px; }
.mode input:checked + span { border-color: var(--accent); background: var(--accent-soft); box-shadow: inset 0 0 0 1px var(--accent); }

.notice { margin: 0 0 12px; padding: 10px 14px; border-radius: 10px; background: var(--surface-2); color: var(--muted); font-size: 14px; }
.foot { text-align: center; margin-top: 18px; }

/* Quiz */
.quiz-bar { display: flex; justify-content: space-between; align-items: center; margin-bottom: 10px; }
.count { color: var(--muted); font-size: 14px; font-variant-numeric: tabular-nums; }
.progress { height: 4px; background: var(--line); border-radius: 2px; overflow: hidden; margin-bottom: 20px; }
.progress-fill { height: 100%; width: 0; background: var(--accent); transition: width 0.25s ease; }

.card {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 24px;
  box-shadow: var(--shadow);
}
.meta { margin: 0 0 8px; color: var(--muted); font-size: 13px; }
.prompt { font-size: 19px; font-weight: 600; margin-bottom: 16px; }

.code {
  margin: 0 0 18px;
  padding: 16px 18px;
  background: var(--code-bg);
  color: var(--code-text);
  border-radius: 10px;
  font: 14.5px/1.6 var(--mono);
  overflow-x: auto;
  tab-size: 4;
}
.code .kw { color: var(--tok-kw); }
.code .str { color: var(--tok-str); }
.code .num { color: var(--tok-num); }
.code .fn { color: var(--tok-fn); }
.code .com { color: var(--tok-com); font-style: italic; }
.code .blank { background: rgb(255 255 255 / 0.12); border-bottom: 2px solid var(--tok-num); border-radius: 3px; padding: 0 4px; }

/* Answer inputs */
.options { display: grid; gap: 8px; }
.opt {
  position: relative;
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 10px;
  cursor: pointer;
  background: var(--surface);
}
.opt:hover { border-color: var(--muted); }
.opt input { position: absolute; opacity: 0; pointer-events: none; }
.opt .key {
  flex: none;
  width: 24px; height: 24px;
  display: grid; place-items: center;
  border-radius: 6px;
  background: var(--surface-2);
  color: var(--muted);
  font: 600 12px var(--mono);
}
.opt .txt { min-width: 0; overflow-wrap: anywhere; }
.opt.selected { border-color: var(--accent); background: var(--accent-soft); }
.opt.selected .key { background: var(--accent); color: var(--accent-text); }
.opt.correct { border-color: var(--good); background: var(--good-soft); }
.opt.correct .key { background: var(--good); color: var(--surface); }
.opt.wrong { border-color: var(--bad); background: var(--bad-soft); }
.opt.wrong .key { background: var(--bad); color: var(--surface); }
.locked .opt { cursor: default; }
.locked .opt:not(.correct):not(.wrong) { opacity: 0.6; }

.text-answer {
  width: 100%;
  font: 15px/1.5 var(--mono);
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--surface);
  color: var(--text);
  resize: vertical;
}
.text-answer:focus { outline: 2px solid var(--accent); outline-offset: 1px; border-color: transparent; }
.text-answer.correct { border-color: var(--good); background: var(--good-soft); }
.text-answer.wrong { border-color: var(--bad); background: var(--bad-soft); }

.actions { display: flex; justify-content: space-between; align-items: center; gap: 12px; margin-top: 18px; }
.hint { color: var(--muted); font-size: 13px; }
.hint kbd, .learn kbd {
  font: 600 11px var(--mono);
  border: 1px solid var(--line);
  border-bottom-width: 2px;
  border-radius: 4px;
  padding: 0 5px;
  background: var(--surface);
}

/* Feedback */
.feedback { margin-top: 16px; border-radius: 10px; padding: 14px 16px; border-left: 4px solid; }
.feedback.good { background: var(--good-soft); border-color: var(--good); }
.feedback.bad { background: var(--bad-soft); border-color: var(--bad); }
.feedback.neutral { background: var(--surface-2); border-color: var(--muted); }
.fb-title { font-weight: 700; margin: 0; }
.fb-answer { margin: 6px 0 0; }
.fb-answer pre { margin: 6px 0 0; font: 14px/1.5 var(--mono); white-space: pre-wrap; }
.explain { margin-top: 10px; }
.explain summary { cursor: pointer; color: var(--accent); font-size: 14px; font-weight: 600; }
.explain p { margin: 8px 0 0; }
.explain .code { margin: 10px 0 0; font-size: 13.5px; }
.ref { margin: 10px 0 0; font-size: 13px; color: var(--muted); }
.ref .link { font-size: 13px; }

/* Results */
.breakdown { list-style: none; margin: 0 0 28px; padding: 0; display: grid; gap: 8px; }
.breakdown li {
  display: grid;
  grid-template-columns: 1fr 120px auto;
  gap: 14px;
  align-items: center;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px 14px;
}
.bar { height: 6px; background: var(--surface-2); border-radius: 3px; overflow: hidden; }
.bar span { display: block; height: 100%; background: var(--accent); }
.bar.low span { background: var(--bad); }
.pct { font-variant-numeric: tabular-nums; font-weight: 600; min-width: 42px; text-align: right; }

.missed { list-style: none; margin: 0; padding: 0; display: grid; gap: 8px; }
.missed > li > details { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); }
.missed > li > details > summary { cursor: pointer; padding: 12px 14px; font-weight: 600; list-style: none; display: flex; gap: 10px; }
.missed > li > details > summary::-webkit-details-marker { display: none; }
.missed > li > details > summary::before { content: "▸"; color: var(--muted); }
.missed > li > details[open] > summary::before { content: "▾"; }
.missed .m-body { padding: 0 14px 14px; }
.missed .code { margin: 0 0 12px; font-size: 13.5px; }
.m-row { margin: 4px 0; font-size: 14px; }
.m-row b { display: inline-block; min-width: 92px; color: var(--muted); font-weight: 500; }
.m-row pre { display: inline; font: 14px var(--mono); white-space: pre-wrap; }

.row { display: flex; gap: 10px; justify-content: flex-end; }
.empty { color: var(--muted); }

/* Concept card */
.learn {
  width: min(640px, calc(100vw - 32px));
  max-height: calc(100vh - 64px);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 24px;
  background: var(--surface);
  color: var(--text);
}
.learn::backdrop { background: rgb(0 0 0 / 0.45); }
.learn-head { display: flex; justify-content: space-between; align-items: flex-start; gap: 12px; margin-bottom: 8px; }
.learn-head h2 { font-size: 22px; }
.learn h3 { font-size: 15px; margin: 18px 0 6px; }
.learn ul { margin: 0; padding-left: 20px; }
.learn li { margin: 4px 0; }
.learn .code { margin: 10px 0 0; font-size: 13.5px; }

@media (max-width: 560px) {
  .app { padding-top: 24px; }
  h1 { font-size: 26px; }
  .modes { grid-template-columns: 1fr; }
  .card { padding: 18px; }
  .prompt { font-size: 17px; }
  .breakdown li { grid-template-columns: 1fr 64px auto; }
  .hint { display: none; }
  .row .btn { flex: 1; }
}

/* Top bar */
.topbar {
  position: sticky;
  top: 0;
  z-index: 5;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  max-width: 720px;
  margin: 0 auto;
  padding: 12px 16px;
  background: var(--bg);
  border-bottom: 1px solid var(--line);
}
.brand { appearance: none; border: 0; background: none; color: var(--text); font: 700 15px/1 inherit; font-family: inherit; cursor: pointer; padding: 4px 0; }
.brand:hover { color: var(--accent); }
.who { display: flex; align-items: center; gap: 8px; font-size: 14px; min-width: 0; }
.who b { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; max-width: 40vw; }
.sync { width: 8px; height: 8px; border-radius: 50%; background: var(--muted); flex: none; }
.sync.ok { background: var(--good); }
.sync.saving { background: var(--tok-num); }
.sync.error { background: var(--bad); }
.app:has(> .screen:not([hidden]):not(#screen-login)) { padding-top: 24px; }

/* Login */
.login { display: flex; gap: 8px; margin-bottom: 12px; }
.login .text-answer { flex: 1; font-family: inherit; font-size: 17px; }
.chips { display: flex; flex-wrap: wrap; gap: 8px; }
.chip {
  appearance: none;
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--text);
  font: inherit;
  font-size: 14px;
  padding: 6px 12px;
  border-radius: 999px;
  cursor: pointer;
}
.chip:hover { border-color: var(--muted); }
.chip.on { background: var(--accent-soft); border-color: var(--accent); color: var(--text); box-shadow: inset 0 0 0 1px var(--accent); }
.chip:focus-visible, .choice:focus-visible, .tab:focus-visible, .brand:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* Home choices */
.choices { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.choice {
  appearance: none;
  text-align: left;
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 22px;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--surface);
  color: var(--text);
  font: inherit;
  cursor: pointer;
  box-shadow: var(--shadow);
}
.choice:hover { border-color: var(--accent); }
.choice-icon { font-size: 26px; line-height: 1; margin-bottom: 4px; }
.choice b { font-size: 20px; }
.choice span:not(.choice-icon) { color: var(--muted); font-size: 14px; }
.choice small { margin-top: auto; padding-top: 10px; color: var(--accent); font-weight: 600; font-size: 13px; }

/* Tabs */
.tabs { display: inline-flex; gap: 4px; padding: 4px; margin-bottom: 20px; background: var(--surface-2); border-radius: 12px; }
.tab { appearance: none; border: 0; background: none; color: var(--muted); font: inherit; font-weight: 600; padding: 8px 18px; border-radius: 9px; cursor: pointer; }
.tab.on { background: var(--surface); color: var(--text); box-shadow: var(--shadow); }

/* Handbook */
.hb-tools { display: grid; gap: 12px; margin-bottom: 8px; }
.search { font-family: inherit; }
.hb-count { color: var(--muted); font-size: 13px; margin: 8px 0 16px; }
.hb-group { margin-bottom: 26px; }
.hb-group-head { display: flex; justify-content: space-between; align-items: baseline; gap: 12px; margin-bottom: 8px; }
.hb-group-head h3 { margin: 0; font-size: 15px; }
.hb-entry { background: var(--surface); border: 1px solid var(--line); border-radius: 10px; margin-bottom: 6px; }
.hb-entry > summary, .hb-entry.plain { display: block; padding: 10px 14px; list-style: none; }
.hb-entry > summary { cursor: pointer; }
.hb-entry > summary::-webkit-details-marker { display: none; }
.hb-entry > summary:hover { background: var(--surface-2); border-radius: 10px; }
.hb-entry[open] > summary { border-bottom: 1px solid var(--line); border-radius: 10px 10px 0 0; }
.hb-line { display: flex; flex-wrap: wrap; align-items: center; gap: 6px; margin-bottom: 2px; }
.hb-name { font-size: 14px; font-weight: 700; background: none; padding: 0; color: var(--accent); }
.hb-text { display: block; font-size: 15px; }
.kind { font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.04em; color: var(--muted); background: var(--surface-2); padding: 1px 6px; border-radius: 4px; }
.kind.bonus { color: var(--tok-num); background: none; border: 1px solid currentColor; }
.known { color: var(--good); font-weight: 700; font-size: 13px; }
.hb-ex { padding: 12px 14px 14px; }
.hb-ex .code, .flash .code { margin: 0; font-size: 13.5px; }
.out-label { margin: 10px 0 4px; font-size: 12px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.04em; color: var(--muted); }
.out { margin: 0; padding: 10px 14px; background: var(--surface-2); border-radius: 8px; font: 13.5px/1.5 var(--mono); white-space: pre-wrap; }

/* Flashcards */
.flash { min-height: 260px; display: flex; flex-direction: column; }
.flash-name { font: 700 30px/1.25 var(--mono); margin: 18px 0 22px; overflow-wrap: anywhere; }
.flash-text { font-size: 18px; margin: 0 0 14px; }
.flash .actions { margin-top: auto; padding-top: 18px; }
#fc-buttons { justify-content: flex-end; }

@media (max-width: 560px) {
  .choices { grid-template-columns: 1fr; }
  .flash-name { font-size: 24px; }
  .login { flex-direction: column; }
}