:root {
  --bg: #f4f5f7;
  --panel: #ffffff;
  --ink: #1c2230;
  --muted: #6b7280;
  --line: #e3e6ec;
  --accent: #e4572e;
  --good: #1a9d54;
  --good-bg: #e6f6ec;
  --bad: #d1354a;
  --bad-bg: #fceaed;
  --shadow: 0 6px 24px rgba(20, 25, 40, .10);
  --radius: 16px;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14171f;
    --panel: #1e222c;
    --ink: #e8ebf2;
    --muted: #9aa3b2;
    --line: #2c313d;
    --accent: #f2703f;
    --good: #4cc487;
    --good-bg: #16352a;
    --bad: #f0748a;
    --bad-bg: #3a1f26;
    --shadow: 0 6px 24px rgba(0, 0, 0, .35);
  }
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }  /* gana a las reglas display:flex/grid de abajo */
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Gate ---------- */
.gate {
  min-height: 100vh; display: flex; align-items: center; justify-content: center; padding: 20px;
}
.gate-box {
  width: 100%; max-width: 360px; background: var(--panel); border: 1px solid var(--line);
  border-radius: var(--radius); box-shadow: var(--shadow); padding: 34px 28px; text-align: center;
  display: flex; flex-direction: column; gap: 12px;
}
.gate-logo { font-size: 40px; }
.gate-box h2 { margin: 0; font-size: 20px; }
.gate-box p { margin: 0; color: var(--muted); font-size: 14px; }
.gate-box input {
  font: inherit; padding: 11px 14px; border-radius: 10px; border: 1px solid var(--line);
  background: var(--bg); color: var(--ink); margin-top: 6px;
}
.gate-box input:focus { outline: 2px solid color-mix(in srgb, var(--accent) 45%, transparent); border-color: var(--accent); }
.gate-error { color: var(--bad) !important; font-size: 13px; }

/* ---------- Topbar ---------- */
.topbar {
  display: flex; align-items: center; justify-content: space-between;
  gap: 16px; padding: 16px 22px; background: var(--panel);
  border-bottom: 1px solid var(--line); position: sticky; top: 0; z-index: 10;
}
.brand { display: flex; align-items: center; gap: 12px; }
.logo { font-size: 30px; }
h1 { font-size: 18px; margin: 0; }
.subtitle { margin: 0; color: var(--muted); font-size: 12.5px; }
.topbar-right { display: flex; align-items: center; gap: 12px; }
.stats { display: flex; gap: 10px; font-size: 13px; }
.stat { padding: 4px 10px; border-radius: 999px; background: var(--bg); border: 1px solid var(--line); }
.stat-known { color: var(--good); }
.stat-unknown { color: var(--bad); }
.stat-pending { color: var(--muted); }

/* ---------- Layout ---------- */
.deck-picker, .study { max-width: 900px; margin: 0 auto; padding: 26px 20px 60px; }
h2 { font-size: 20px; margin: 4px 0 18px; }

/* ---------- Deck grid ---------- */
.deck-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 14px; }
.deck-card {
  text-align: left; cursor: pointer; border: 1px solid var(--line);
  background: var(--panel); border-radius: var(--radius); padding: 18px;
  box-shadow: var(--shadow); transition: transform .12s ease, border-color .12s ease;
  display: flex; flex-direction: column; gap: 8px;
}
.deck-card:hover { transform: translateY(-3px); border-color: var(--accent); }
.deck-card.all { border-color: var(--accent); background: linear-gradient(160deg, var(--panel), color-mix(in srgb, var(--accent) 8%, var(--panel))); }
.deck-emoji { font-size: 26px; }
.deck-name { font-weight: 650; font-size: 15px; }
.deck-meta { color: var(--muted); font-size: 12.5px; }

/* ---------- Study head ---------- */
.study-head { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; margin-bottom: 14px; }
.deck-title { font-weight: 650; font-size: 15px; margin-right: auto; }
.study-tools { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; }
.chk { font-size: 13px; color: var(--muted); display: inline-flex; align-items: center; gap: 6px; cursor: pointer; }

/* ---------- Buttons ---------- */
.btn {
  font: inherit; cursor: pointer; border-radius: 10px; padding: 8px 14px;
  border: 1px solid var(--line); background: var(--panel); color: var(--ink);
  transition: transform .08s ease, background .12s ease;
}
.btn:hover { transform: translateY(-1px); }
.btn:active { transform: translateY(0); }
.btn.ghost { background: transparent; }
.btn.primary { background: var(--accent); color: #fff; border-color: transparent; font-weight: 650; padding: 11px 14px; }
.btn.good { background: var(--good-bg); border-color: transparent; color: var(--good); font-weight: 650; }
.btn.bad { background: var(--bad-bg); border-color: transparent; color: var(--bad); font-weight: 650; }

/* ---------- Progress ---------- */
.progress { display: flex; align-items: center; gap: 12px; margin-bottom: 16px; }
.progress-bar { flex: 1; height: 8px; background: var(--panel); border: 1px solid var(--line); border-radius: 99px; overflow: hidden; }
.progress-bar > span { display: block; height: 100%; width: 0; background: var(--accent); transition: width .2s ease; }
.progress-text { font-size: 13px; color: var(--muted); min-width: 64px; text-align: right; }

/* ---------- Card ---------- */
.card-area { display: flex; align-items: stretch; gap: 12px; }
.card { flex: 1; min-height: 320px; cursor: pointer; perspective: 1400px; background: transparent; border: none; padding: 0; }
.card:focus { outline: none; }
.card:focus-visible .card-inner { box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 45%, transparent), var(--shadow); }
.card-inner {
  height: 100%; min-height: 320px; background: var(--panel); border: 1px solid var(--line);
  border-radius: var(--radius); box-shadow: var(--shadow); padding: 30px 30px 34px;
  display: flex; flex-direction: column; justify-content: center;
  transition: transform .18s ease, opacity .18s ease;
}
.card.flipping .card-inner { transform: rotateX(90deg); opacity: 0; }
.card.is-answer .card-inner { border-color: color-mix(in srgb, var(--accent) 35%, var(--line)); }
.card-face { display: flex; flex-direction: column; gap: 16px; }
.badge {
  align-self: flex-start; font-size: 11px; letter-spacing: .04em; text-transform: uppercase;
  color: var(--muted); background: var(--bg); border: 1px solid var(--line);
  padding: 3px 10px; border-radius: 99px; font-weight: 600;
}
.badge.answer { color: var(--accent); border-color: color-mix(in srgb, var(--accent) 40%, var(--line)); }
.card-q { font-size: 20px; font-weight: 650; }
.card-a { font-size: 15.5px; }
.card-a p { margin: 0 0 10px; }
.card-a ul { margin: 6px 0; padding-left: 20px; }
.card-a code { font-family: ui-monospace, SFMono-Regular, Menlo, monospace; font-size: .9em; background: var(--bg); border: 1px solid var(--line); border-radius: 6px; padding: 1px 5px; }
.card-a strong { color: var(--ink); }
.flip-hint { color: var(--muted); font-size: 12.5px; margin-top: 4px; }
.card.graded-good .card-inner { border-left: 4px solid var(--good); }
.card.graded-bad .card-inner { border-left: 4px solid var(--bad); }

.nav-btn {
  flex: 0 0 46px; border: 1px solid var(--line); background: var(--panel); color: var(--ink);
  border-radius: 12px; font-size: 26px; cursor: pointer; box-shadow: var(--shadow);
  transition: background .12s ease;
}
.nav-btn:hover { background: var(--bg); }
.nav-btn:disabled { opacity: .35; cursor: default; }

/* ---------- Grade + shortcuts ---------- */
.grade { display: flex; gap: 12px; justify-content: center; margin-top: 18px; }
.grade .btn { padding: 11px 22px; font-size: 15px; }
.shortcuts { display: flex; gap: 16px; flex-wrap: wrap; justify-content: center; margin-top: 26px; color: var(--muted); font-size: 12px; }
kbd { font-family: inherit; background: var(--panel); border: 1px solid var(--line); border-bottom-width: 2px; border-radius: 6px; padding: 1px 6px; font-size: 11px; margin: 0 1px; }

@media (max-width: 560px) {
  .nav-btn { flex-basis: 38px; font-size: 22px; }
  .card-inner { padding: 22px; min-height: 280px; }
  .card-q { font-size: 18px; }
  .stats { display: none; }
}