:root {
  --bg-primary: #0a0a0f;
  --bg-secondary: #14141f;
  --bg-tertiary: #1e1e2e;
  --text-primary: #ffffff;
  --text-secondary: #a0a0b0;
  --text-muted: #606070;
  --accent: #00d4ff;
  --accent-secondary: #00ff88;
  --danger: #ff4466;
  --focus-ring: #00d4ff;
  --focus-glow: rgba(0, 212, 255, 0.4);
  --radius-md: 12px;
}
* { margin: 0; padding: 0; box-sizing: border-box; }
html, body {
  width: 600px; height: 600px; overflow: hidden;
  background: #000;
  color: var(--text-primary);
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}
#app { width: 100%; height: 100%; position: relative; }
.screen { width: 100%; height: 100%; position: absolute; top: 0; left: 0; display: flex; flex-direction: column; }
.screen.hidden { display: none; }
.focusable { transition: all 0.15s ease; border: 2px solid transparent; cursor: pointer; outline: none; }
.focusable:focus { border-color: var(--focus-ring); box-shadow: 0 0 20px var(--focus-glow); }
.hidden { display: none !important; }

/* ---- Header ---- */
.hdr {
  background: var(--bg-secondary);
  padding: 24px 28px;
  border-bottom: 1px solid var(--bg-tertiary);
  flex-shrink: 0;
}
.hdr h1 { font-size: 38px; font-weight: 800; letter-spacing: 1px; }
.hdr .sub { color: var(--accent); font-size: 18px; margin-top: 6px; letter-spacing: 2px; }
.hdr-row { display: flex; align-items: center; gap: 18px; padding: 18px 24px; }
.hdr-row h2 { font-size: 26px; font-weight: 700; }

.backbtn {
  background: var(--bg-tertiary);
  color: var(--text-primary);
  font-size: 20px;
  font-weight: 600;
  padding: 0 22px;
  height: 52px;
  border-radius: var(--radius-md);
  display: inline-flex;
  align-items: center;
  flex-shrink: 0;
}

/* ---- Home menu ---- */
.menu {
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 22px;
  padding: 0 36px;
}
.card {
  display: flex;
  align-items: center;
  gap: 22px;
  background: var(--bg-primary);
  border-radius: var(--radius-md);
  padding: 24px 28px;
  min-height: 96px;
  text-align: left;
}
.card-ico {
  width: 64px; height: 64px;
  flex-shrink: 0;
  background: var(--bg-tertiary);
  color: var(--accent);
  border-radius: var(--radius-md);
  display: flex; align-items: center; justify-content: center;
  font-size: 34px; font-weight: 800;
}
.card-txt { display: flex; flex-direction: column; gap: 4px; }
.card-title { font-size: 28px; font-weight: 700; color: var(--text-primary); }
.card-desc { font-size: 17px; color: var(--text-secondary); }

.foot {
  flex-shrink: 0;
  padding: 18px 36px 26px;
  color: var(--text-secondary);
  font-size: 17px;
}

/* ---- Reference list ---- */
.ref-list {
  flex: 1;
  overflow-y: auto;
  padding: 16px 24px 24px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}
.ref-list::-webkit-scrollbar { width: 8px; }
.ref-list::-webkit-scrollbar-thumb { background: var(--bg-tertiary); border-radius: 4px; }
.ref-item {
  display: flex;
  align-items: center;
  gap: 20px;
  background: var(--bg-primary);
  border-radius: var(--radius-md);
  padding: 14px 22px;
  min-height: 72px;
}
.ref-letter {
  width: 56px; height: 56px;
  flex-shrink: 0;
  background: var(--bg-tertiary);
  color: var(--accent);
  border-radius: var(--radius-md);
  display: flex; align-items: center; justify-content: center;
  font-size: 30px; font-weight: 800;
}
.ref-word { font-size: 28px; font-weight: 700; flex: 1; }
.ref-pron { font-size: 18px; color: var(--text-secondary); letter-spacing: 0.5px; }

/* ---- Drill ---- */
.drill-score {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  margin-left: auto;
  gap: 2px;
}
#drill-streak { font-size: 20px; font-weight: 700; color: var(--accent-secondary); }
#drill-tally { font-size: 16px; color: var(--text-secondary); }

.drill-body {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 14px 32px 28px;
}
.drill-q { font-size: 20px; color: var(--text-secondary); margin-top: 6px; }
.drill-letter {
  font-size: 120px;
  font-weight: 800;
  line-height: 1.05;
  color: var(--accent);
  margin: 6px 0 18px;
}
.drill-options {
  width: 100%;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}
.opt {
  background: var(--bg-primary);
  color: var(--text-primary);
  border-radius: var(--radius-md);
  min-height: 80px;
  font-size: 26px;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
}
.opt.correct {
  background: rgba(0, 255, 136, 0.18);
  border-color: var(--accent-secondary);
  box-shadow: 0 0 20px rgba(0, 255, 136, 0.35);
}
.opt.wrong {
  background: rgba(255, 68, 102, 0.18);
  border-color: var(--danger);
  box-shadow: 0 0 20px rgba(255, 68, 102, 0.35);
}
.drill-feedback {
  margin-top: 20px;
  font-size: 22px;
  font-weight: 700;
  min-height: 28px;
}
.drill-feedback.ok { color: var(--accent-secondary); }
.drill-feedback.no { color: var(--danger); }