:root {
  --bg: #0f1420; --card: #171d2c; --card2: #1f2637; --text: #eef1f8; --muted: #9aa4bd;
  --accent: #5b8cff; --good: #34c98f; --bad: #ff5d6c; --warn: #ffb648; --border: #2a3348;
}
* { box-sizing: border-box; }
body {
  margin: 0; font-family: 'Sarabun', -apple-system, system-ui, sans-serif;
  background: var(--bg); color: var(--text); min-height: 100vh;
}
a { color: var(--accent); }
.wrap { max-width: 640px; margin: 0 auto; padding: 16px 16px 90px; }
header.top {
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px 16px; border-bottom: 1px solid var(--border); position: sticky; top: 0;
  background: var(--bg); z-index: 5;
}
header.top h1 { font-size: 18px; margin: 0; }
header.top .streak { font-size: 14px; color: var(--warn); }

.card { background: var(--card); border: 1px solid var(--border); border-radius: 16px; padding: 18px; margin-bottom: 14px; }
.card2 { background: var(--card2); border-radius: 12px; padding: 14px; }

.btn {
  display: block; width: 100%; padding: 16px; font-size: 17px; font-weight: 700;
  border-radius: 14px; border: none; cursor: pointer; text-align: center;
  background: var(--accent); color: white; margin-top: 8px;
}
.btn:disabled { opacity: .5; }
.btn.secondary { background: var(--card2); color: var(--text); border: 1px solid var(--border); }
.btn.good { background: var(--good); }
.btn.bad { background: var(--bad); }

.choice {
  display: block; width: 100%; text-align: left; padding: 14px 16px; margin: 8px 0;
  border-radius: 12px; border: 1px solid var(--border); background: var(--card2); color: var(--text);
  font-size: 15px; cursor: pointer; line-height: 1.5;
}
.choice:hover { border-color: var(--accent); }
.choice.correct { border-color: var(--good); background: #123527; }
.choice.wrong { border-color: var(--bad); background: #3a1a1e; }

.timer { font-size: 32px; font-weight: 800; text-align: center; margin: 10px 0; font-variant-numeric: tabular-nums; }
.timer.low { color: var(--bad); }

.stem { white-space: pre-wrap; font-size: 16px; line-height: 1.7; font-family: Georgia, 'Times New Roman', serif; }
.tag { display: inline-block; font-size: 12px; padding: 3px 9px; border-radius: 999px; background: var(--card2); color: var(--muted); margin-right: 6px; }

.hanzi { font-size: 26px; line-height: 1.8; margin-bottom: 6px; }
.pinyin { color: var(--muted); font-size: 15px; margin-bottom: 14px; }
.choice .hz { font-size: 19px; margin-right: 8px; }
.choice .py { color: var(--muted); font-size: 13px; }

.muted { color: var(--muted); font-size: 14px; }
.center { text-align: center; }
.row { display: flex; gap: 10px; }
.row > * { flex: 1; }

nav.tabs {
  position: fixed; bottom: 0; left: 0; right: 0; display: flex;
  background: var(--card); border-top: 1px solid var(--border); z-index: 10;
}
nav.tabs button {
  flex: 1; background: none; border: none; color: var(--muted); padding: 12px 4px;
  font-size: 12px; cursor: pointer;
}
nav.tabs button.active { color: var(--accent); font-weight: 700; }
nav.tabs .ic { display: block; font-size: 20px; margin-bottom: 2px; }

input, textarea {
  width: 100%; padding: 12px 14px; border-radius: 10px; border: 1px solid var(--border);
  background: var(--card2); color: var(--text); font-size: 15px;
}
label { font-size: 14px; color: var(--muted); display: block; margin: 10px 0 4px; }

table { width: 100%; border-collapse: collapse; font-size: 14px; }
th, td { padding: 8px; text-align: left; border-bottom: 1px solid var(--border); }

.hidden { display: none !important; }
.err { color: var(--bad); font-size: 14px; margin-top: 8px; }
.spin { text-align: center; padding: 40px 0; color: var(--muted); }
.explain { background: var(--card2); border-radius: 12px; padding: 14px; margin-top: 12px; font-size: 14px; line-height: 1.7; }
.explain b { color: var(--accent); }

.bar-row { display: flex; align-items: center; gap: 8px; margin: 6px 0; font-size: 13px; }
.bar-track { flex: 1; height: 10px; border-radius: 6px; background: var(--card2); overflow: hidden; }
.bar-fill { height: 100%; background: var(--accent); }
.flash { perspective: 1000px; }
.flash-inner { position: relative; min-height: 160px; display: flex; align-items: center; justify-content: center;
  text-align: center; padding: 20px; font-size: 20px; border-radius: 16px; background: var(--card2); cursor: pointer; }