:root {
  --bg: #fafafa;
  --bg-elev: #ffffff;
  --bg-elev-2: #f4f4f5;
  --fg: #18181b;
  --fg-muted: #52525b;
  --fg-subtle: #a1a1aa;
  --border: #e4e4e7;
  --border-strong: #d4d4d8;
  --accent: #4f46e5;
  --accent-fg: #ffffff;
  --accent-soft: #eef2ff;
  --good: #16a34a;
  --warn: #d97706;
  --bad: #dc2626;
  --easy: #2563eb;
  --shadow-1: 0 1px 2px rgba(0,0,0,.04), 0 1px 3px rgba(0,0,0,.06);
  --shadow-2: 0 4px 12px rgba(0,0,0,.06), 0 2px 4px rgba(0,0,0,.04);
  --radius: 12px;
  --radius-lg: 18px;
  --maxw: 1040px;
  --font: -apple-system, BlinkMacSystemFont, "Inter", "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --font-display: ui-serif, "Iowan Old Style", "Apple Garamond", "Palatino", Georgia, serif;
  --font-mono: ui-monospace, SFMono-Regular, "JetBrains Mono", Menlo, Consolas, monospace;
}

[data-theme="dark"] {
  --bg: #0b0b0e;
  --bg-elev: #16161b;
  --bg-elev-2: #1f1f26;
  --fg: #ededf0;
  --fg-muted: #a1a1aa;
  --fg-subtle: #71717a;
  --border: #27272f;
  --border-strong: #3f3f46;
  --accent: #818cf8;
  --accent-fg: #0b0b0e;
  --accent-soft: #1e1b4b;
  --good: #4ade80;
  --warn: #fbbf24;
  --bad: #f87171;
  --easy: #60a5fa;
  --shadow-1: 0 1px 2px rgba(0,0,0,.4);
  --shadow-2: 0 4px 16px rgba(0,0,0,.45);
}

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

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

body {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

button { font: inherit; color: inherit; cursor: pointer; }

h1, h2, h3 { font-family: var(--font-display); font-weight: 600; letter-spacing: -0.01em; }
h1 { font-size: 2rem; margin: 0 0 .25em; }
h2 { font-size: 1.4rem; margin: 0 0 .25em; }
h3 { font-size: 1.1rem; margin: 0 0 .25em; }

/* ---------- topbar ---------- */
.topbar {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  padding: .9rem clamp(1rem, 4vw, 2rem);
  border-bottom: 1px solid var(--border);
  background: var(--bg-elev);
  position: sticky;
  top: 0;
  z-index: 5;
  backdrop-filter: saturate(140%) blur(8px);
}
.brand {
  display: flex; align-items: center; gap: .55rem;
  color: var(--fg);
  font-weight: 600;
  letter-spacing: -0.01em;
}
.brand:hover { text-decoration: none; }
.brand svg { color: var(--accent); }
.nav { display: flex; gap: 1.25rem; margin-left: auto; }
.nav a {
  color: var(--fg-muted);
  font-size: .95rem;
  padding: .25rem 0;
  border-bottom: 2px solid transparent;
}
.nav a:hover { color: var(--fg); text-decoration: none; }
.nav a.active { color: var(--fg); border-bottom-color: var(--accent); }
.topbar-actions { display: flex; align-items: center; gap: .5rem; }
.icon-btn {
  border: 1px solid var(--border);
  background: var(--bg-elev-2);
  color: var(--fg-muted);
  border-radius: 999px;
  width: 34px; height: 34px;
  display: inline-flex; align-items: center; justify-content: center;
  transition: background .15s ease, color .15s ease, border-color .15s ease;
}
.icon-btn:hover { color: var(--fg); border-color: var(--border-strong); }

/* ---------- layout ---------- */
.app {
  flex: 1;
  width: 100%;
  max-width: var(--maxw);
  margin: 0 auto;
  padding: clamp(1rem, 4vw, 2.5rem);
}
.loading { color: var(--fg-muted); padding: 4rem 0; text-align: center; }

.footer {
  border-top: 1px solid var(--border);
  color: var(--fg-subtle);
  font-size: .85rem;
  padding: 1.25rem clamp(1rem, 4vw, 2rem);
  text-align: center;
  background: var(--bg-elev);
}
.footer a { color: var(--fg-muted); }

/* ---------- buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  padding: .65rem 1.1rem;
  border-radius: var(--radius);
  border: 1px solid var(--border-strong);
  background: var(--bg-elev);
  color: var(--fg);
  font-weight: 500;
  font-size: .95rem;
  transition: transform .04s ease, background .15s ease, border-color .15s ease, color .15s ease;
}
.btn:hover { background: var(--bg-elev-2); }
.btn:active { transform: translateY(1px); }
.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--accent-fg);
}
.btn-primary:hover { background: color-mix(in srgb, var(--accent) 88%, black); }
.btn-ghost { background: transparent; border-color: transparent; color: var(--fg-muted); }
.btn-ghost:hover { color: var(--fg); background: var(--bg-elev-2); }
.btn-block { width: 100%; justify-content: center; }
.btn-sm { padding: .4rem .75rem; font-size: .85rem; }

/* ---------- home ---------- */
.hero {
  margin-bottom: 2rem;
}
.hero p {
  color: var(--fg-muted);
  max-width: 60ch;
  margin: 0;
}
.hero .pill {
  display: inline-block;
  font-size: .8rem;
  font-weight: 500;
  padding: .25rem .65rem;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent);
  margin-bottom: .8rem;
  letter-spacing: .02em;
  text-transform: uppercase;
}

.deck-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0;
}
.deck-card {
  display: flex;
  flex-direction: column;
  gap: .75rem;
  padding: 1.25rem;
  border-radius: var(--radius-lg);
  background: var(--bg-elev);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-1);
  text-align: left;
  cursor: pointer;
  transition: transform .12s ease, box-shadow .12s ease, border-color .12s ease;
  color: inherit;
}
.deck-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-2);
  border-color: var(--border-strong);
  text-decoration: none;
}
.deck-card.deck-card-featured { border-color: color-mix(in srgb, var(--accent) 35%, var(--border)); }
.deck-card-head {
  display: flex; justify-content: space-between; align-items: flex-start; gap: .5rem;
}
.deck-card h3 { margin: 0; }
.deck-card p { margin: 0; color: var(--fg-muted); font-size: .9rem; }
.deck-card .deck-stats {
  display: flex; gap: 1rem; font-size: .85rem; color: var(--fg-muted);
  border-top: 1px solid var(--border); padding-top: .75rem; margin-top: auto;
}
.deck-card .deck-stats strong { color: var(--fg); font-weight: 600; }

.locale-tag {
  font-size: .75rem;
  font-weight: 500;
  letter-spacing: .05em;
  text-transform: uppercase;
  color: var(--fg-subtle);
  border: 1px solid var(--border);
  padding: .15rem .45rem;
  border-radius: 6px;
}

.import-box {
  margin-top: 2rem;
  padding: 1.25rem;
  border: 1px dashed var(--border-strong);
  border-radius: var(--radius);
  background: var(--bg-elev);
}
.import-box h3 { margin: 0 0 .25rem; }
.import-box p { color: var(--fg-muted); margin: 0 0 .75rem; font-size: .9rem; }
.import-box textarea {
  width: 100%;
  min-height: 120px;
  font-family: var(--font-mono);
  font-size: .85rem;
  padding: .75rem;
  border-radius: 8px;
  border: 1px solid var(--border-strong);
  background: var(--bg);
  color: var(--fg);
  resize: vertical;
}
.import-box .actions { display: flex; gap: .5rem; margin-top: .75rem; flex-wrap: wrap; }
.import-error { color: var(--bad); font-size: .85rem; margin-top: .5rem; }

/* ---------- deck detail ---------- */
.deck-header {
  display: flex; gap: 1.5rem; align-items: flex-start; flex-wrap: wrap;
  margin-bottom: 1.5rem;
}
.deck-header .meta { flex: 1; min-width: 250px; }
.deck-header .meta p { color: var(--fg-muted); margin: .25rem 0 0; }
.deck-header .actions { display: flex; gap: .5rem; flex-wrap: wrap; }

.summary-row {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: .75rem;
  margin: 1.5rem 0;
}
.summary-stat {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
}
.summary-stat .label {
  font-size: .8rem; color: var(--fg-muted); text-transform: uppercase; letter-spacing: .05em;
  margin-bottom: .35rem;
}
.summary-stat .value { font-size: 1.6rem; font-weight: 600; font-family: var(--font-display); }
.summary-stat.due .value { color: var(--accent); }
.summary-stat.new .value { color: var(--good); }
.summary-stat.learning .value { color: var(--warn); }

.unit-list { display: flex; flex-direction: column; gap: .6rem; margin-top: 1rem; }
.unit-row {
  display: grid;
  grid-template-columns: 1fr auto auto;
  align-items: center;
  gap: 1rem;
  padding: .85rem 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-elev);
}
.unit-row .name { font-weight: 500; }
.unit-row .blurb { color: var(--fg-muted); font-size: .85rem; margin-top: .15rem; }
.unit-row .progress {
  width: 160px;
  height: 6px;
  background: var(--bg-elev-2);
  border-radius: 999px;
  overflow: hidden;
  position: relative;
}
.unit-row .progress > span {
  display: block;
  height: 100%;
  background: linear-gradient(90deg, var(--accent), color-mix(in srgb, var(--accent) 50%, var(--good)));
}
.unit-row .count { font-variant-numeric: tabular-nums; color: var(--fg-muted); font-size: .85rem; min-width: 64px; text-align: right; }

.settings-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}
.settings-grid label {
  display: flex;
  flex-direction: column;
  gap: .35rem;
  font-size: .9rem;
  color: var(--fg-muted);
}
.settings-grid input, .settings-grid select {
  padding: .5rem .65rem;
  border-radius: 8px;
  border: 1px solid var(--border-strong);
  background: var(--bg-elev);
  color: var(--fg);
  font: inherit;
}

/* ---------- study session ---------- */
.session {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.5rem;
  min-height: 60vh;
}
.session-header {
  display: flex; gap: 1rem; align-items: center; width: 100%;
  font-size: .9rem; color: var(--fg-muted);
}
.session-header .progress-bar {
  flex: 1;
  height: 5px;
  background: var(--bg-elev-2);
  border-radius: 999px;
  overflow: hidden;
}
.session-header .progress-bar > span {
  display: block; height: 100%; background: var(--accent);
  transition: width .25s ease;
}
.session-header .leave { margin-left: auto; }

.card {
  width: 100%;
  max-width: 640px;
  min-height: 320px;
  background: var(--bg-elev);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  box-shadow: var(--shadow-2);
  display: flex;
  flex-direction: column;
  padding: 2.5rem clamp(1rem, 4vw, 2.5rem) 1.5rem;
  position: relative;
  cursor: pointer;
  user-select: none;
  transition: transform .25s cubic-bezier(.2,.8,.2,1), opacity .15s ease;
}
.card.flipping { transform: rotateY(8deg); opacity: 0; }
.card .pos {
  position: absolute;
  top: 1rem; left: 1.25rem;
  font-size: .75rem;
  color: var(--fg-subtle);
  text-transform: uppercase;
  letter-spacing: .08em;
}
.card .speak {
  position: absolute;
  top: .85rem; right: 1rem;
  border: 1px solid var(--border);
  background: var(--bg-elev-2);
  color: var(--fg-muted);
  border-radius: 999px;
  width: 36px; height: 36px;
  display: inline-flex; align-items: center; justify-content: center;
}
.card .speak:hover { color: var(--fg); }
.card .front-text {
  font-family: var(--font-display);
  font-size: clamp(1.8rem, 5vw, 2.8rem);
  font-weight: 500;
  text-align: center;
  margin: auto 0;
  padding: 1rem 0;
  word-break: break-word;
  flex-shrink: 0;
}
.card .back {
  border-top: 1px solid var(--border);
  margin-top: 1.5rem;
  padding-top: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: .5rem;
}
.card .back-text {
  font-size: 1.3rem;
  font-weight: 500;
  color: var(--fg);
}
.card .example {
  font-size: .95rem;
  color: var(--fg-muted);
  font-style: italic;
}
.card .example .ex-back { color: var(--fg-subtle); font-style: normal; display: block; margin-top: .15rem; }
.card .notes { font-size: .85rem; color: var(--fg-subtle); margin-top: .5rem; }
.card .hint {
  font-size: .8rem;
  color: var(--fg-subtle);
  letter-spacing: .04em;
  text-align: center;
  margin-top: auto;
  padding-top: 1.5rem;
}

.grade-prompt {
  text-align: center;
  color: var(--fg-muted);
  font-size: .9rem;
  margin: 0 0 .75rem;
}
.grade-row {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: .65rem;
  width: 100%;
  max-width: 640px;
}
.grade-btn {
  border: 1px solid var(--border-strong);
  background: var(--bg-elev);
  color: var(--fg);
  border-radius: var(--radius);
  padding: .85rem .5rem;
  display: flex; flex-direction: column; align-items: center; gap: .15rem;
  font-weight: 500;
  font-size: .95rem;
  transition: background .12s ease, border-color .12s ease, transform .04s ease;
}
.grade-btn:hover { background: var(--bg-elev-2); }
.grade-btn:active { transform: translateY(1px); }
.grade-btn .grade-hint { font-size: .73rem; color: var(--fg-muted); font-weight: 400; }
.grade-btn .interval { font-size: .75rem; color: var(--fg-subtle); font-weight: 400; }
.grade-btn .key { font-size: .7rem; color: var(--fg-subtle); font-family: var(--font-mono); }
.grade-btn[data-grade="0"] { border-color: color-mix(in srgb, var(--bad) 30%, var(--border-strong)); }
.grade-btn[data-grade="0"]:hover { background: color-mix(in srgb, var(--bad) 8%, var(--bg-elev)); }
.grade-btn[data-grade="3"] { border-color: color-mix(in srgb, var(--warn) 30%, var(--border-strong)); }
.grade-btn[data-grade="3"]:hover { background: color-mix(in srgb, var(--warn) 8%, var(--bg-elev)); }
.grade-btn[data-grade="4"] { border-color: color-mix(in srgb, var(--good) 30%, var(--border-strong)); }
.grade-btn[data-grade="4"]:hover { background: color-mix(in srgb, var(--good) 8%, var(--bg-elev)); }
.grade-btn[data-grade="5"] { border-color: color-mix(in srgb, var(--easy) 30%, var(--border-strong)); }
.grade-btn[data-grade="5"]:hover { background: color-mix(in srgb, var(--easy) 8%, var(--bg-elev)); }

.session-done {
  text-align: center;
  padding: 3rem 1rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
  align-items: center;
}
.session-done .big-num {
  font-family: var(--font-display);
  font-size: 4rem;
  font-weight: 600;
  color: var(--accent);
  line-height: 1;
}

/* ---------- stats ---------- */
.stats-overall {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 1rem;
  margin-bottom: 2rem;
}
.heatmap {
  display: grid;
  grid-template-columns: repeat(53, 1fr);
  gap: 3px;
  margin: 1rem 0;
}
.heatmap .cell {
  aspect-ratio: 1;
  border-radius: 2px;
  background: var(--bg-elev-2);
}
.heatmap .cell[data-level="1"] { background: color-mix(in srgb, var(--accent) 25%, var(--bg-elev-2)); }
.heatmap .cell[data-level="2"] { background: color-mix(in srgb, var(--accent) 50%, var(--bg-elev-2)); }
.heatmap .cell[data-level="3"] { background: color-mix(in srgb, var(--accent) 75%, var(--bg-elev-2)); }
.heatmap .cell[data-level="4"] { background: var(--accent); }

/* ---------- about ---------- */
.about {
  max-width: 70ch;
}
.about h2 { margin-top: 1.75rem; }
.about p, .about li { color: var(--fg); }
.about .muted { color: var(--fg-muted); }
.about pre {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: .75rem;
  overflow-x: auto;
  font-size: .85rem;
  font-family: var(--font-mono);
}

/* ---------- empty/error ---------- */
.empty {
  text-align: center;
  color: var(--fg-muted);
  padding: 3rem 1rem;
}
.empty h2 { color: var(--fg); }
.banner-error {
  background: color-mix(in srgb, var(--bad) 10%, var(--bg-elev));
  border: 1px solid color-mix(in srgb, var(--bad) 30%, var(--border));
  color: color-mix(in srgb, var(--bad) 80%, var(--fg));
  padding: .75rem 1rem;
  border-radius: 8px;
  margin: 1rem 0;
  font-size: .9rem;
}

/* ---------- dialog ---------- */
.dialog {
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  background: var(--bg-elev);
  color: var(--fg);
  box-shadow: var(--shadow-2);
  max-width: 90vw;
}
.dialog::backdrop { background: rgba(0,0,0,.4); backdrop-filter: blur(2px); }
.kbd-table { border-collapse: collapse; margin: 1rem 0; font-size: .9rem; }
.kbd-table td { padding: .35rem 1rem .35rem 0; }
kbd {
  font-family: var(--font-mono);
  background: var(--bg-elev-2);
  border: 1px solid var(--border-strong);
  border-bottom-width: 2px;
  border-radius: 4px;
  padding: .1rem .4rem;
  font-size: .85rem;
}

/* ---------- responsive ---------- */
@media (max-width: 640px) {
  .nav { gap: .9rem; font-size: .9rem; }
  .topbar { gap: .75rem; padding: .75rem 1rem; }
  .grade-row { grid-template-columns: repeat(2, 1fr); }
  .deck-header .actions { width: 100%; }
  .deck-header .actions .btn { flex: 1; justify-content: center; }
  .unit-row { grid-template-columns: 1fr auto; }
  .unit-row .progress { display: none; }
}