:root {
  --bg: #f5f6fa;
  --surface: #ffffff;
  --text: #1c2233;
  --muted: #667085;
  --border: #e3e6ee;
  --accent: #3b5bdb;
  --accent-soft: #e7ecff;
  --good: #2f9e44;
  --good-soft: #e6f6ea;
  --bad: #e03131;
  --bad-soft: #fdecec;
  --shadow: 0 6px 24px rgba(20, 30, 60, .08);
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #12151d;
    --surface: #1b1f2a;
    --text: #e8eaf0;
    --muted: #98a0b3;
    --border: #2b3140;
    --accent: #7b93ff;
    --accent-soft: #232b48;
    --good: #51cf66;
    --good-soft: #1d3324;
    --bad: #ff6b6b;
    --bad-soft: #3a2024;
    --shadow: 0 6px 24px rgba(0, 0, 0, .35);
  }
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
}
.wrap { max-width: 720px; margin: 0 auto; padding: 0 16px; }
.muted { color: var(--muted); }
.center { text-align: center; justify-content: center; }

.top { background: var(--surface); border-bottom: 1px solid var(--border); position: sticky; top: 0; z-index: 5; }
.top-inner { display: flex; align-items: center; justify-content: space-between; padding-top: 12px; padding-bottom: 8px; }
.brand { font-weight: 700; font-size: 1.1rem; display: flex; align-items: center; gap: 10px; }
.logo { background: var(--accent); color: #fff; border-radius: 8px; padding: 2px 7px; font-size: .9rem; }
.stats { display: flex; gap: 14px; font-size: .95rem; }
.tabs { display: flex; gap: 4px; overflow-x: auto; }
.tab {
  border: 0; background: none; color: var(--muted); font: inherit; font-weight: 600;
  padding: 10px 12px; border-bottom: 3px solid transparent; cursor: pointer; white-space: nowrap;
}
.tab.active { color: var(--accent); border-bottom-color: var(--accent); }

main { padding-top: 20px; padding-bottom: 24px; }
.toolbar { display: flex; justify-content: flex-end; margin-bottom: 16px; }
.toolbar label { display: flex; align-items: center; gap: 8px; color: var(--muted); font-size: .95rem; }
select, input[type=text] {
  font: inherit; color: var(--text); background: var(--surface);
  border: 1px solid var(--border); border-radius: 10px; padding: 8px 12px;
}
input[type=text] { min-width: 0; flex: 1; max-width: 280px; }
select:focus, input:focus { outline: 2px solid var(--accent); outline-offset: 1px; }

.panel { display: none; }
.panel.active { display: block; }
.row { display: flex; gap: 10px; flex-wrap: wrap; margin: 14px 0; }

.btn {
  font: inherit; font-weight: 600; border: 0; border-radius: 10px; padding: 10px 18px;
  background: var(--accent); color: #fff; cursor: pointer; transition: transform .1s, opacity .2s;
}
.btn:active { transform: scale(.97); }
.btn.ghost { background: var(--accent-soft); color: var(--accent); }
.btn.good { background: var(--good); }
.btn.bad { background: var(--bad); }
.btn.big { font-size: 1.15rem; padding: 14px 26px; }

.box { background: var(--surface); border: 1px solid var(--border); border-radius: 16px; padding: 22px; box-shadow: var(--shadow); }
.question { font-size: 1.5rem; margin: 6px 0 18px; }
.options { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
@media (max-width: 480px) { .options { grid-template-columns: 1fr; } }
.option {
  font: inherit; text-align: left; padding: 12px 14px; border-radius: 10px; cursor: pointer;
  border: 1px solid var(--border); background: var(--bg); color: var(--text);
}
.option:hover:not(:disabled) { border-color: var(--accent); }
.option.correct { background: var(--good-soft); border-color: var(--good); }
.option.wrong { background: var(--bad-soft); border-color: var(--bad); }
.option:disabled { cursor: default; }
.feedback { min-height: 1.5em; font-weight: 600; margin: 14px 0 0; }
.feedback.ok { color: var(--good); }
.feedback.no { color: var(--bad); }

/* Flashcard */
.card-scene { perspective: 1000px; max-width: 420px; margin: 0 auto; }
.flashcard {
  position: relative; width: 100%; height: 240px; border: 0; padding: 0; background: none;
  font: inherit; color: inherit; cursor: pointer; transform-style: preserve-3d; transition: transform .5s;
}
.flashcard.flipped { transform: rotateY(180deg); }
.face {
  position: absolute; inset: 0; display: flex; flex-direction: column; align-items: center; justify-content: center;
  gap: 10px; padding: 20px; border-radius: 18px; background: var(--surface); border: 1px solid var(--border);
  box-shadow: var(--shadow); backface-visibility: hidden; -webkit-backface-visibility: hidden;
}
.back { transform: rotateY(180deg); background: var(--accent-soft); }
.word { font-size: 2rem; font-weight: 700; text-align: center; }
.hint { color: var(--muted); font-size: .85rem; }
.example { color: var(--muted); font-style: italic; text-align: center; }

footer { padding: 24px 16px 40px; font-size: .9rem; }