/* ---------- tokens ---------- */

:root {
  --bg: #f7f5f2;
  --bg-raised: #ffffff;
  --bg-sunken: #efece7;
  --ink: #1e1c19;
  --ink-soft: #56514a;
  --ink-faint: #8b857c;
  --line: #e2ddd5;
  --line-strong: #cdc6bb;
  --accent: #2f6f5e;
  --accent-ink: #ffffff;
  --accent-soft: #e4efea;
  --danger: #a33a2b;
  --ok: #2f7d4f;
  --warn: #9a6a1f;
  --new: #3a6ea5;
  --radius: 12px;
  --radius-lg: 18px;
  --shadow: 0 1px 2px rgba(30, 28, 25, .05), 0 6px 24px -12px rgba(30, 28, 25, .18);
  --font-ui: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Inter, Roboto, sans-serif;
  --font-read: ui-serif, Georgia, "Iowan Old Style", "Times New Roman", serif;
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  --wrap: 62rem;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14161a;
    --bg-raised: #1b1e24;
    --bg-sunken: #101216;
    --ink: #e8e6e1;
    --ink-soft: #a9a49c;
    --ink-faint: #7b766e;
    --line: #2a2e36;
    --line-strong: #3a3f49;
    --accent: #5eb99c;
    --accent-ink: #0f1a17;
    --accent-soft: #1d2c28;
    --danger: #e0705e;
    --ok: #62b981;
    --warn: #d0a24e;
    --new: #7aa9dd;
    --shadow: 0 1px 2px rgba(0, 0, 0, .3), 0 10px 30px -14px rgba(0, 0, 0, .6);
  }
}

:root[data-theme="light"] {
  --bg: #f7f5f2; --bg-raised: #fff; --bg-sunken: #efece7;
  --ink: #1e1c19; --ink-soft: #56514a; --ink-faint: #8b857c;
  --line: #e2ddd5; --line-strong: #cdc6bb;
  --accent: #2f6f5e; --accent-ink: #fff; --accent-soft: #e4efea;
  --danger: #a33a2b; --ok: #2f7d4f; --warn: #9a6a1f; --new: #3a6ea5;
  --shadow: 0 1px 2px rgba(30, 28, 25, .05), 0 6px 24px -12px rgba(30, 28, 25, .18);
}

:root[data-theme="dark"] {
  --bg: #14161a; --bg-raised: #1b1e24; --bg-sunken: #101216;
  --ink: #e8e6e1; --ink-soft: #a9a49c; --ink-faint: #7b766e;
  --line: #2a2e36; --line-strong: #3a3f49;
  --accent: #5eb99c; --accent-ink: #0f1a17; --accent-soft: #1d2c28;
  --danger: #e0705e; --ok: #62b981; --warn: #d0a24e; --new: #7aa9dd;
  --shadow: 0 1px 2px rgba(0, 0, 0, .3), 0 10px 30px -14px rgba(0, 0, 0, .6);
}

/* ---------- base ---------- */

*, *::before, *::after { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-ui);
  font-size: 16px;
  line-height: 1.55;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  min-height: 100dvh;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4 { line-height: 1.2; margin: 0 0 .4em; font-weight: 640; letter-spacing: -.015em; }
h1 { font-size: clamp(1.6rem, 1.2rem + 1.6vw, 2.2rem); }
h2 { font-size: 1.15rem; }
h3 { font-size: 1.05rem; }
p { margin: 0 0 .8em; }
a { color: var(--accent); text-decoration-color: color-mix(in srgb, var(--accent) 35%, transparent); text-underline-offset: 2px; }
a:hover { text-decoration-color: currentColor; }
img { max-width: 100%; height: auto; border-radius: 8px; display: block; }
hr { border: 0; border-top: 1px solid var(--line); margin: 1.2em 0; }
code, pre, .mono { font-family: var(--font-mono); }
code { font-size: .89em; background: var(--bg-sunken); padding: .12em .35em; border-radius: 5px; }
pre.code { margin: .8em 0; padding: .9em 1em; background: var(--bg-sunken); border: 1px solid var(--line); border-radius: var(--radius); overflow-x: auto; font-size: .86rem; line-height: 1.5; }
pre.code code { background: none; padding: 0; font-size: inherit; }
blockquote { margin: .8em 0; padding: .1em 0 .1em 1em; border-left: 3px solid var(--line-strong); color: var(--ink-soft); }
ul, ol { margin: 0 0 .8em; padding-left: 1.3em; }
li { margin: .2em 0; }
mark { background: color-mix(in srgb, var(--warn) 30%, transparent); color: inherit; padding: 0 .15em; border-radius: 3px; }
.muted { color: var(--ink-soft); }
.small { font-size: .86rem; }
.sub { color: var(--ink-soft); font-size: 1.02rem; }
.math-raw { font-family: var(--font-mono); font-size: .9em; color: var(--ink-soft); }

::selection { background: color-mix(in srgb, var(--accent) 30%, transparent); }

:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 6px; }

/* ---------- chrome ---------- */

.topbar {
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: .7rem clamp(1rem, 4vw, 2rem);
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(10px);
  position: sticky;
  top: 0;
  z-index: 20;
}
.brand { display: flex; align-items: center; gap: .5rem; font-weight: 680; color: var(--ink); text-decoration: none; letter-spacing: -.02em; }
.brand-mark { font-size: 1.15rem; }
.nav { display: flex; gap: .25rem; margin-left: auto; flex-wrap: wrap; }
.nav a {
  color: var(--ink-soft); text-decoration: none; font-size: .92rem; font-weight: 520;
  padding: .35rem .7rem; border-radius: 99px;
}
.nav a:hover { background: var(--bg-sunken); color: var(--ink); }
.nav a.active { background: var(--accent-soft); color: var(--accent); }
.icon-btn {
  background: none; border: 1px solid var(--line); color: var(--ink-soft);
  width: 2rem; height: 2rem; border-radius: 99px; cursor: pointer; line-height: 1;
  display: grid; place-items: center; font-size: .95rem;
}
.icon-btn:hover { background: var(--bg-sunken); color: var(--ink); }

.view { flex: 1; width: 100%; max-width: var(--wrap); margin: 0 auto; padding: clamp(1.2rem, 3vw, 2.4rem) clamp(1rem, 4vw, 2rem) 3rem; }

.footer {
  border-top: 1px solid var(--line); padding: 1rem clamp(1rem, 4vw, 2rem);
  color: var(--ink-faint); font-size: .82rem; text-align: center;
}

.crumbs { font-size: .85rem; color: var(--ink-faint); margin-bottom: .8rem; }
.crumbs a { color: var(--ink-soft); text-decoration: none; }
.crumbs a:hover { color: var(--accent); }
.crumbs span { margin: 0 .35rem; }

/* ---------- buttons ---------- */

.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: .4rem;
  font: inherit; font-size: .92rem; font-weight: 550;
  padding: .5rem 1rem; border-radius: 10px;
  border: 1px solid var(--line-strong); background: var(--bg-raised); color: var(--ink);
  cursor: pointer; text-decoration: none; transition: background .12s, border-color .12s, transform .06s;
}
.btn:hover { background: var(--bg-sunken); }
.btn:active { transform: translateY(1px); }
.btn[disabled] { opacity: .45; cursor: not-allowed; }
.btn-primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.btn-primary:hover { background: color-mix(in srgb, var(--accent) 85%, black); }
.btn-danger { color: var(--danger); border-color: color-mix(in srgb, var(--danger) 40%, var(--line)); }
.btn-danger:hover { background: color-mix(in srgb, var(--danger) 12%, transparent); }
.btn-lg { padding: .7rem 1.6rem; font-size: 1rem; border-radius: 12px; }
.btn-sm { padding: .3rem .7rem; font-size: .84rem; border-radius: 8px; }
.row { display: flex; flex-wrap: wrap; gap: .6rem; }

.input {
  font: inherit; padding: .5rem .7rem; border-radius: 10px;
  border: 1px solid var(--line-strong); background: var(--bg-raised); color: var(--ink);
  width: 100%; max-width: 100%;
}
.input:focus { outline: 2px solid var(--accent); outline-offset: 0; border-color: transparent; }

/* ---------- home ---------- */

.hero {
  display: flex; gap: 2rem; align-items: center; justify-content: space-between;
  padding: clamp(1.2rem, 3vw, 2rem); margin-bottom: 2rem;
  background: var(--bg-raised); border: 1px solid var(--line);
  border-radius: var(--radius-lg); box-shadow: var(--shadow);
}
.hero-text { min-width: 0; }
.hero h1 { margin-bottom: .2em; }
.stat-row { display: flex; flex-wrap: wrap; gap: 1.4rem; margin: 1.1rem 0 1.3rem; }
.stat-row.centered { justify-content: center; margin-bottom: 1.6rem; }
.stat { display: flex; flex-direction: column; }
.stat-n { font-size: 1.5rem; font-weight: 660; letter-spacing: -.02em; line-height: 1.1; }
.stat-l { font-size: .78rem; color: var(--ink-faint); text-transform: uppercase; letter-spacing: .05em; }

.hero-ring { position: relative; flex: none; width: 116px; height: 116px; display: grid; place-items: center; }
.ring { width: 116px; height: 116px; transform: rotate(-90deg); }
.ring circle { fill: none; stroke-width: 3; }
.ring-bg { stroke: var(--line); }
.ring-fg { stroke: var(--accent); stroke-linecap: round; transition: stroke-dasharray .5s ease; }
.ring-label { position: absolute; text-align: center; line-height: 1.15; }
.ring-label b { display: block; font-size: 1.25rem; letter-spacing: -.02em; }
.ring-label span { font-size: .7rem; color: var(--ink-faint); text-transform: uppercase; letter-spacing: .05em; }

.deck-grid { display: grid; gap: 1rem; grid-template-columns: repeat(auto-fill, minmax(17rem, 1fr)); }
.deck {
  display: flex; flex-direction: column; gap: .7rem;
  background: var(--bg-raised); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 1.1rem; box-shadow: var(--shadow);
  transition: border-color .15s, transform .1s;
}
.deck:hover { border-color: var(--line-strong); }
.deck-head { text-decoration: none; color: inherit; }
.deck-head h3 { margin-bottom: .2em; }
.deck-head p { margin: 0; color: var(--ink-soft); font-size: .88rem; }
.deck-badges { display: flex; gap: .4rem; flex-wrap: wrap; }
.deck-foot { display: flex; align-items: center; justify-content: space-between; gap: .5rem; margin-top: auto; font-size: .85rem; }
.deck-actions { display: flex; gap: .4rem; }

.pill { font-size: .74rem; font-weight: 600; padding: .2rem .55rem; border-radius: 99px; letter-spacing: .01em; }
.pill-due { background: color-mix(in srgb, var(--accent) 16%, transparent); color: var(--accent); }
.pill-new { background: color-mix(in srgb, var(--new) 16%, transparent); color: var(--new); }
.pill-done { background: var(--bg-sunken); color: var(--ink-faint); }

.bar { height: 5px; background: var(--bg-sunken); border-radius: 99px; overflow: hidden; }
.bar span { display: block; height: 100%; background: var(--accent); border-radius: 99px; transition: width .3s ease; }
.bar.thin { height: 3px; margin-bottom: 1.6rem; }

/* ---------- browse ---------- */

.page-head { display: flex; gap: 1rem; align-items: flex-start; justify-content: space-between; flex-wrap: wrap; margin-bottom: 1.2rem; }
.page-head-actions { display: flex; gap: .5rem; }
.toolbar { margin-bottom: 1rem; }

.card-list { display: flex; flex-direction: column; gap: .5rem; }
.browse-card { background: var(--bg-raised); border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; }
.browse-card summary {
  display: flex; align-items: flex-start; gap: 1rem; justify-content: space-between;
  padding: .8rem 1rem; cursor: pointer; list-style: none;
}
.browse-card summary::-webkit-details-marker { display: none; }
.browse-card summary:hover { background: var(--bg-sunken); }
.browse-front { min-width: 0; font-family: var(--font-read); }
.browse-front :is(p, ul, ol) { margin: 0; }
.browse-front p + p { margin-top: .4em; }
.browse-meta { display: flex; gap: .35rem; flex: none; align-items: center; }
.browse-back { padding: 0 1rem 1rem; border-top: 1px solid var(--line); padding-top: .9rem; font-family: var(--font-read); }

.tag {
  font-size: .72rem; font-weight: 600; padding: .15rem .5rem; border-radius: 99px;
  background: var(--bg-sunken); color: var(--ink-faint); white-space: nowrap;
}
.tag-mc { color: var(--new); background: color-mix(in srgb, var(--new) 14%, transparent); }
.tag-cloze { color: var(--warn); background: color-mix(in srgb, var(--warn) 16%, transparent); }
.tag-new { color: var(--new); background: color-mix(in srgb, var(--new) 14%, transparent); }
.tag-review { color: var(--ok); background: color-mix(in srgb, var(--ok) 14%, transparent); }
.tag-learning, .tag-relearning { color: var(--warn); background: color-mix(in srgb, var(--warn) 16%, transparent); }
.card-tags { display: flex; gap: .35rem; flex-wrap: wrap; margin-top: .8rem; }

.choices.static { list-style: none; padding: 0; margin: 0 0 .6em; }
.choices.static li { display: flex; gap: .55rem; align-items: baseline; padding: .2rem 0; }
.choices.static .tick { flex: none; font-weight: 700; }
.choices.static .is-correct { color: var(--ok); }
.choices.static .is-wrong { color: var(--ink-faint); }
.choices.static :is(p) { margin: 0; }

/* ---------- study ---------- */

.study { max-width: 44rem; margin: 0 auto; }
.study-top { display: flex; align-items: center; justify-content: space-between; gap: 1rem; margin-bottom: .6rem; }
.back { color: var(--ink-soft); text-decoration: none; font-size: .9rem; }
.back:hover { color: var(--accent); }
.study-counts { display: flex; align-items: center; gap: .6rem; font-size: .85rem; }

.card {
  background: var(--bg-raised); border: 1px solid var(--line);
  border-radius: var(--radius-lg); box-shadow: var(--shadow);
  padding: clamp(1.3rem, 4vw, 2.4rem);
  font-family: var(--font-read);
  font-size: 1.12rem;
  min-height: 12rem;
  display: flex; flex-direction: column; gap: .2rem;
}
.card-deck { font-family: var(--font-ui); font-size: .74rem; text-transform: uppercase; letter-spacing: .06em; color: var(--ink-faint); margin-bottom: .6rem; }
.card-front { font-size: 1.16em; }
.card-front :is(p):last-child { margin-bottom: 0; }
.card-rule { border-top: 1px dashed var(--line-strong); margin: 1.2em 0; }
.answer { color: var(--ink); }
.answer :is(p):last-child, .explain :is(p):last-child { margin-bottom: 0; }
.explain { margin-top: 1em; padding: .8em 1em; background: var(--bg-sunken); border-radius: var(--radius); font-size: .95em; }
.cloze { background: color-mix(in srgb, var(--warn) 22%, transparent); border-radius: 5px; padding: 0 .3em; color: var(--ink-soft); font-style: italic; }
.cloze.revealed { background: color-mix(in srgb, var(--accent) 20%, transparent); color: var(--accent); font-style: normal; font-weight: 600; }
.cloze-answer { font-family: var(--font-read); }

.choices { list-style: none; margin: 1.2em 0 0; padding: 0; display: flex; flex-direction: column; gap: .5rem; }
.choice {
  width: 100%; display: flex; gap: .7rem; align-items: baseline; text-align: left;
  font: inherit; font-size: .95rem; font-family: var(--font-read);
  padding: .7rem .9rem; border-radius: 10px; cursor: pointer;
  background: var(--bg); border: 1px solid var(--line-strong); color: var(--ink);
  transition: background .12s, border-color .12s;
}
.choice:hover:not(:disabled) { border-color: var(--accent); background: var(--accent-soft); }
.choice-key {
  flex: none; font-family: var(--font-ui); font-size: .72rem; font-weight: 700;
  width: 1.4rem; height: 1.4rem; border-radius: 6px; display: inline-grid; place-items: center;
  background: var(--bg-sunken); color: var(--ink-faint); align-self: center;
}
.choice-text :is(p) { margin: 0; }
.choice.picked { border-color: var(--accent); background: var(--accent-soft); }
.choice.picked .choice-key { background: var(--accent); color: var(--accent-ink); }
.choice.checked { cursor: default; opacity: 1; }
.choice.correct { border-color: var(--ok); background: color-mix(in srgb, var(--ok) 12%, transparent); }
.choice.correct .choice-key { background: var(--ok); color: #fff; }
.choice.wrong { border-color: var(--danger); background: color-mix(in srgb, var(--danger) 10%, transparent); }
.choice.wrong .choice-key { background: var(--danger); color: #fff; }
.choice:disabled { opacity: .85; }

.verdict { font-family: var(--font-ui); font-weight: 640; font-size: .95rem; margin-top: 1.1em; }
.verdict.ok { color: var(--ok); }
.verdict.no { color: var(--danger); }

.controls { margin-top: 1.4rem; display: flex; justify-content: center; }
.ratings { display: grid; grid-template-columns: repeat(4, 1fr); gap: .5rem; width: 100%; }
.rate { flex-direction: column; gap: .1rem; padding: .6rem .4rem; }
.rate-label { font-weight: 600; }
.rate-ivl { font-size: .76rem; color: var(--ink-faint); font-variant-numeric: tabular-nums; }
.rate-key { display: none; }
.rate-again:hover { border-color: var(--danger); color: var(--danger); }
.rate-hard:hover { border-color: var(--warn); color: var(--warn); }
.rate-good:hover { border-color: var(--accent); color: var(--accent); }
.rate-easy:hover { border-color: var(--ok); color: var(--ok); }
.hints { text-align: center; color: var(--ink-faint); font-size: .8rem; margin-top: .9rem; }

.done { text-align: center; max-width: 34rem; margin: 3rem auto; }
.done-mark {
  width: 3.4rem; height: 3.4rem; border-radius: 99px; margin: 0 auto 1.2rem;
  display: grid; place-items: center; font-size: 1.6rem;
  background: var(--accent-soft); color: var(--accent);
}
.done-actions { display: flex; gap: .6rem; justify-content: center; flex-wrap: wrap; }

/* ---------- settings, misc ---------- */

.panel { background: var(--bg-raised); border: 1px solid var(--line); border-radius: var(--radius); padding: 1.2rem; margin-bottom: 1rem; }
.panel h2 { margin-bottom: .8rem; }
.field { display: flex; align-items: center; justify-content: space-between; gap: 1rem; margin-bottom: .7rem; font-size: .92rem; }
.field .input { max-width: 8rem; }
.check { display: flex; align-items: center; gap: .5rem; font-size: .92rem; margin-bottom: .7rem; }
.keys { display: grid; grid-template-columns: auto 1fr; gap: .4rem 1rem; margin: 0; font-size: .9rem; }
.keys dt { font-family: var(--font-mono); font-size: .82rem; color: var(--ink-soft); white-space: nowrap; }
.keys dd { margin: 0; color: var(--ink-soft); }

.empty { text-align: center; padding: 3rem 1rem; color: var(--ink-soft); }
.empty.small { padding: 1.5rem; }
.loading { display: flex; align-items: center; justify-content: center; gap: .6rem; padding: 4rem 1rem; color: var(--ink-faint); }
.spinner {
  width: 1rem; height: 1rem; border-radius: 99px;
  border: 2px solid var(--line-strong); border-top-color: var(--accent);
  animation: spin .7s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

.toast {
  position: fixed; left: 50%; bottom: 1.5rem; transform: translate(-50%, 1rem);
  background: var(--ink); color: var(--bg); padding: .55rem 1rem; border-radius: 99px;
  font-size: .87rem; opacity: 0; pointer-events: none; transition: opacity .2s, transform .2s; z-index: 50;
}
.toast.show { opacity: 1; transform: translate(-50%, 0); }

.katex-display { overflow-x: auto; overflow-y: hidden; padding: .2em 0; }

/* ---------- responsive ---------- */

@media (max-width: 640px) {
  .hero { flex-direction: column-reverse; align-items: flex-start; gap: 1.2rem; }
  .hero-ring { align-self: center; }
  .ratings { grid-template-columns: repeat(2, 1fr); }
  .page-head-actions, .deck-actions { width: 100%; }
  .browse-card summary { flex-direction: column; gap: .5rem; }
  .nav a { padding: .35rem .55rem; }
  .card { font-size: 1.06rem; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: .01ms !important; transition-duration: .01ms !important; }
}