:root {
  color-scheme: dark;
  --bg: #14141b;
  --surface: #1e1e28;
  --surface-2: #262633;
  --text: #ececf4;
  --muted: #9a9aad;
  --border: #2e2e3d;
  --accent: #8b7dff;
  --accent-ink: #ffffff;
  --good: #21b573;
  --bad: #e8556d;
  --shadow: 0 1px 2px rgba(0, 0, 0, .3), 0 10px 30px rgba(0, 0, 0, .35);
  --radius: 14px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  line-height: 1.5;
}

/* ---------- top bar ---------- */
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 12px 18px;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}
.brand {
  display: flex;
  align-items: center;
  gap: 8px;
  background: none;
  border: none;
  cursor: pointer;
  font-size: 18px;
  font-weight: 700;
  color: var(--text);
  padding: 0;
}
.brand-logo { font-size: 22px; }
.topnav { display: flex; gap: 8px; }
.topnav button {
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 8px 14px;
  border-radius: 10px;
  cursor: pointer;
  font-size: 14px;
  font-weight: 600;
}
.topnav button:hover { border-color: var(--accent); }
.review-btn { position: relative; }
.badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 18px;
  height: 18px;
  padding: 0 5px;
  margin-left: 4px;
  border-radius: 999px;
  background: var(--accent);
  color: var(--accent-ink);
  font-size: 11px;
  font-weight: 700;
}

/* ---------- layout ---------- */
.app {
  flex: 1;
  width: 100%;
  max-width: 780px;
  margin: 0 auto;
  padding: 24px 18px 48px;
}
.footer {
  text-align: center;
  color: var(--muted);
  font-size: 13px;
  padding: 16px;
  border-top: 1px solid var(--border);
}
.linklike {
  background: none;
  border: none;
  color: var(--accent);
  cursor: pointer;
  font: inherit;
  padding: 0;
}
.linklike:hover { text-decoration: underline; }

/* ---------- headings / rows ---------- */
.page-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 18px;
}
.page-head h1 { font-size: 24px; margin: 0; }
.page-head .sub { color: var(--muted); font-size: 14px; }
.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: none;
  border: none;
  color: var(--muted);
  cursor: pointer;
  font-size: 14px;
  padding: 0 0 12px;
}
.back-link:hover { color: var(--accent); }

/* ---------- buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 16px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
}
.btn:hover { border-color: var(--accent); }
.btn.primary { background: var(--accent); color: var(--accent-ink); border-color: var(--accent); }
.btn.primary:hover { filter: brightness(1.05); }
.btn.ghost { background: transparent; }
.btn.small { padding: 6px 10px; font-size: 13px; }
.btn.danger { color: var(--bad); border-color: transparent; }
.btn.danger:hover { border-color: var(--bad); }
.btn:disabled { opacity: .45; cursor: not-allowed; }

/* ---------- group cards ---------- */
.group-grid { display: grid; gap: 12px; }
.group-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 18px;
  box-shadow: var(--shadow);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  cursor: pointer;
}
.group-card:hover { border-color: var(--accent); }
.group-card .g-info h3 { margin: 0 0 2px; font-size: 17px; }
.group-card .g-meta { color: var(--muted); font-size: 13px; }
.group-card .g-actions { display: flex; gap: 6px; flex-shrink: 0; }

/* ---------- card list (manage) ---------- */
.card-row {
  display: grid;
  grid-template-columns: 1fr 1fr auto;
  gap: 10px;
  align-items: center;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 12px;
  margin-bottom: 8px;
}
.card-row .side { font-size: 14px; overflow-wrap: anywhere; }
.card-row .side.back { color: var(--muted); }
.card-row .r-actions { display: flex; gap: 4px; }
@media (max-width: 520px) {
  .card-row { grid-template-columns: 1fr auto; }
  .card-row .side.back { grid-column: 1 / -1; border-top: 1px dashed var(--border); padding-top: 6px; }
}

/* ---------- forms ---------- */
.field { margin-bottom: 12px; }
.field label { display: block; font-size: 13px; color: var(--muted); margin-bottom: 4px; }
input[type="text"], textarea {
  width: 100%;
  padding: 10px 12px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--surface-2);
  color: var(--text);
  font: inherit;
  resize: vertical;
}
input[type="text"]:focus, textarea:focus {
  outline: none;
  border-color: var(--accent);
  background: var(--surface);
}
.row-inline { display: flex; gap: 8px; flex-wrap: wrap; }
.row-inline .grow { flex: 1; min-width: 160px; }

/* ---------- empty state ---------- */
.empty {
  text-align: center;
  color: var(--muted);
  padding: 48px 16px;
}
.empty .big { font-size: 46px; margin-bottom: 8px; }

/* ---------- flashcard (browse / quiz / review) ---------- */
.study-wrap { text-align: center; }
.study-meta { color: var(--muted); font-size: 14px; margin-bottom: 14px; }
.progressbar {
  height: 6px;
  background: var(--surface-2);
  border-radius: 999px;
  overflow: hidden;
  margin-bottom: 20px;
}
.progressbar > span {
  display: block;
  height: 100%;
  background: var(--accent);
  transition: width .25s ease;
}
.flashcard {
  position: relative;
  width: 100%;
  min-height: 260px;
  perspective: 1400px;
  cursor: pointer;
  margin-bottom: 18px;
}
.flashcard-inner {
  position: relative;
  width: 100%;
  min-height: 260px;
  transition: transform .5s;
  transform-style: preserve-3d;
}
.flashcard.flipped .flashcard-inner { transform: rotateY(180deg); }
.face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 28px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}
.face .face-label {
  position: absolute;
  top: 12px;
  left: 16px;
  font-size: 11px;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--muted);
}
.face .content {
  font-size: 24px;
  font-weight: 600;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
}
.face.back { transform: rotateY(180deg); }
.tap-hint { color: var(--muted); font-size: 13px; margin-top: 12px; }

.study-controls {
  display: flex;
  gap: 10px;
  justify-content: center;
  flex-wrap: wrap;
}
.judge { display: flex; gap: 12px; justify-content: center; }
.judge .btn { min-width: 130px; font-size: 16px; padding: 14px 18px; }
.btn.good { color: var(--good); border-color: var(--good); }
.btn.good:hover { background: var(--good); color: #fff; }
.btn.bad { color: var(--bad); border-color: var(--bad); }
.btn.bad:hover { background: var(--bad); color: #fff; }

/* ---------- group picker (quiz/review) ---------- */
.picker { display: grid; gap: 8px; margin-bottom: 18px; }
.picker label {
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 14px;
  cursor: pointer;
}
.picker label:hover { border-color: var(--accent); }
.picker input { width: 18px; height: 18px; accent-color: var(--accent); }
.picker .count { margin-left: auto; color: var(--muted); font-size: 13px; }

.toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--text);
  color: var(--bg);
  padding: 10px 18px;
  border-radius: 999px;
  font-size: 14px;
  box-shadow: var(--shadow);
  opacity: 0;
  pointer-events: none;
  transition: opacity .2s;
  z-index: 50;
}
.toast.show { opacity: 1; }