:root {
  --bg: #f2f2f7;
  --card: #ffffff;
  --ink: #1c1c1e;
  --muted: #8e8e93;
  --accent: #2f6fed;
  --accent-dark: #1f54c0;
  --good: #34c759;
  --line: #d8d8de;
  --subtle: var(--subtle);
  --radius: 18px;
  --shadow: 0 1px 3px rgba(0,0,0,.08), 0 8px 24px rgba(0,0,0,.06);
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #000000;
    --card: #1c1c1e;
    --ink: #f2f2f7;
    --muted: #98989f;
    --accent: #4f8bff;
    --accent-dark: #2f6fed;
    --good: #30d158;
    --line: #38383a;
    --subtle: #2c2c2e;
    --shadow: 0 1px 3px rgba(0,0,0,.5), 0 8px 24px rgba(0,0,0,.4);
  }
  .key:active { background: #38383a; }
  .sticky-chip { background: rgba(255,159,10,.2); color: #ffb340; }
}

* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; touch-action: manipulation; }

html, body {
  margin: 0;
  height: 100%;
  background: var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif;
  overscroll-behavior: none;
}

body { -webkit-user-select: none; user-select: none; }

.screen { display: none; height: 100dvh; flex-direction: column; }
.screen.active { display: flex; }

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  background: none;
  color: inherit;
}

.muted { color: var(--muted); }

/* ── Home ── */
.home-header { padding: 32px 24px 8px; text-align: center; }
.home-title { margin: 0; font-size: 2.4rem; font-weight: 800; letter-spacing: -.02em; }
.home-sub { margin: 6px 0 0; color: var(--muted); font-size: 1.05rem; }

#roster-grid {
  flex: 1;
  align-content: start;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  gap: 14px;
  padding: 24px;
  overflow-y: auto;
}
.name-btn {
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 22px 14px;
  font-size: 1.25rem;
  font-weight: 600;
  text-align: center;
  transition: transform .08s ease;
}
.name-btn:active { transform: scale(.96); }

#roster-empty { flex: 1; display: flex; flex-direction: column; justify-content: center; align-items: center; text-align: center; }
#roster-empty p { margin: 4px; font-size: 1.2rem; }

#teacher-link {
  margin: 0 auto 24px;
  color: var(--muted);
  font-size: .95rem;
  padding: 10px 16px;
}

/* ── Quiz ── */
.quiz-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 20px 8px;
}
.icon-btn { width: 44px; height: 44px; border-radius: 50%; background: var(--card); box-shadow: var(--shadow); display: grid; place-items: center; }
.icon-btn svg { width: 22px; height: 22px; fill: var(--muted); }
.quiz-timer { font-size: 1.8rem; font-weight: 700; font-variant-numeric: tabular-nums; }
.quiz-timer.low { color: #ff3b30; }
.quiz-score {
  min-width: 56px; text-align: center;
  font-size: 1.5rem; font-weight: 800; color: var(--accent);
  background: var(--card); border-radius: 14px; padding: 6px 10px; box-shadow: var(--shadow);
}

#timer-track { height: 6px; background: var(--line); margin: 8px 20px 0; border-radius: 3px; overflow: hidden; }
#timer-bar { height: 100%; width: 100%; background: var(--accent); transition: width 1s linear; }

.quiz-body { flex: 1; display: flex; align-items: center; justify-content: center; padding: 12px; }
.question {
  font-size: clamp(3rem, 14vw, 6rem);
  font-weight: 800;
  letter-spacing: -.02em;
  display: flex;
  align-items: baseline;
  gap: .25em;
  font-variant-numeric: tabular-nums;
}
.question.long { font-size: clamp(2rem, 8vw, 3.6rem); gap: .15em; }
.question.flash-good { color: var(--good); }
.question.flash-bad { color: #ff3b30; animation: shake .3s ease; }
@keyframes shake { 0%, 100% { transform: translateX(0); } 25% { transform: translateX(-7px); } 75% { transform: translateX(7px); } }
.q-op, .q-eq { color: var(--muted); }
.q-word { font-size: .5em; color: var(--muted); font-weight: 700; align-self: center; }
.q-answer { color: var(--accent); min-width: .6em; }

.keypad {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
  padding: 12px 16px max(20px, env(safe-area-inset-bottom));
  max-width: 460px;
  width: 100%;
  margin: 0 auto;
}
.key {
  background: var(--card);
  border-radius: 16px;
  box-shadow: var(--shadow);
  font-size: 2rem;
  font-weight: 600;
  padding: 18px 0;
  transition: transform .06s ease, background .06s ease;
}
.key:active { transform: scale(.94); background: var(--subtle); }
.key.key-del svg { width: 34px; height: 34px; fill: var(--muted); }
.key.key-del { display: grid; place-items: center; }
.key.key-go { background: var(--good); display: grid; place-items: center; }
.key.key-go svg { width: 36px; height: 36px; fill: #fff; }
.key.key-go:active { background: #2ba84a; }

/* ── Results ── */
#screen-results { align-items: center; justify-content: center; }
#results-panel {
  background: var(--card);
  border-radius: 28px;
  box-shadow: var(--shadow);
  padding: 36px 32px;
  text-align: center;
  width: min(420px, 88vw);
}
#results-emoji { font-size: 3.5rem; }
#results-name { margin: 8px 0 0; font-size: 1.4rem; }
.results-score-big { margin: 8px 0 0; font-size: 5rem; font-weight: 800; color: var(--accent); line-height: 1; }
.results-label { margin: 4px 0 0; color: var(--muted); }
.results-best { margin: 16px 0 0; font-weight: 600; min-height: 1.2em; }
.results-best.pb { color: var(--good); }
.results-actions { display: flex; gap: 12px; margin-top: 28px; }
.results-actions button {
  flex: 1; padding: 14px; border-radius: 14px; font-size: 1.05rem; font-weight: 600;
}
#results-again { background: var(--accent); color: #fff; }
#results-done { background: var(--subtle); }

/* ── Nav bar (teacher) ── */
.nav-bar {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  padding: 14px 16px;
  border-bottom: 1px solid var(--line);
  background: var(--card);
}
.nav-bar h2 { margin: 0; font-size: 1.15rem; }
.back-btn { display: flex; align-items: center; gap: 4px; color: var(--accent); font-size: 1.05rem; justify-self: start; }
.back-btn svg { width: 22px; height: 22px; fill: var(--accent); }

/* ── Teacher content ── */
#teacher-content { flex: 1; overflow-y: auto; padding: 20px 18px 40px; }
.t-section {
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
  margin: 0 0 18px;
}
.t-section h3 { margin: 0 0 12px; font-size: 1.05rem; }
.t-section .hint { color: var(--muted); font-size: .9rem; margin: -6px 0 12px; }

.level-head { margin: 14px 0 8px; font-size: .78rem; font-weight: 700; text-transform: uppercase; letter-spacing: .04em; color: var(--muted); }
.act-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 10px; margin-bottom: 6px; }
.act-chip {
  border: 2px solid var(--line);
  border-radius: 12px;
  padding: 16px 12px;
  text-align: center;
  font-weight: 600;
}
.act-chip.on { border-color: var(--accent); background: var(--accent); color: #fff; }

.chip-row { display: flex; flex-wrap: wrap; gap: 10px; }
.action-chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  border: 2px solid var(--line);
  border-radius: 12px;
  padding: 12px 18px;
  font-weight: 600;
  transition: transform .08s ease;
}
.action-chip:active { transform: scale(.96); }
.action-chip.on { border-color: var(--accent); background: var(--accent); color: #fff; }
.action-chip.danger { border-color: #ff3b30; color: #ff3b30; }

.tables-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(64px, 1fr)); gap: 10px; }
.t-section .hint b { color: var(--ink); }
.table-chip {
  border: 2px solid var(--line);
  border-radius: 12px;
  padding: 12px 0;
  text-align: center;
  font-weight: 600;
  font-size: 1.1rem;
}
.table-chip.on { border-color: var(--accent); background: var(--accent); color: #fff; }

.roster-list { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 12px; }
.roster-pill {
  display: inline-flex; align-items: center; gap: 8px;
  background: var(--subtle); border-radius: 20px; padding: 8px 8px 8px 14px; font-weight: 600;
}
.roster-pill button { color: var(--muted); font-size: 1.3rem; line-height: 1; width: 24px; height: 24px; }
.add-row { display: flex; gap: 8px; }
.add-row input { flex: 1; padding: 12px 14px; border: 1px solid var(--line); border-radius: 12px; font-size: 1rem; background: var(--bg); }
.add-row button, .t-btn {
  background: var(--accent); color: #fff; border-radius: 12px; padding: 12px 18px; font-weight: 600;
}
.t-btn.ghost { background: var(--subtle); color: var(--ink); }
.t-actions { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 6px; }

/* progress cards */
.progress-card { border-top: 1px solid var(--line); padding: 16px 0 4px; }
.progress-card:first-of-type { border-top: none; padding-top: 0; }
.pc-head { display: flex; justify-content: space-between; align-items: baseline; }
.pc-name { font-weight: 700; font-size: 1.1rem; }
.pc-meta { color: var(--muted); font-size: .9rem; }
.runchart { width: 100%; height: 90px; margin-top: 8px; display: block; }
.no-data { color: var(--muted); font-size: .95rem; }

.sticky-chips { display: flex; flex-wrap: wrap; gap: 8px; }
.sticky-chip { background: #fff2e8; color: #c2410c; border-radius: 10px; padding: 8px 12px; font-weight: 700; font-variant-numeric: tabular-nums; }

/* ── PIN overlay ── */
#pin-overlay {
  position: fixed; inset: 0; background: rgba(0,0,0,.45);
  display: flex; align-items: center; justify-content: center; z-index: 50;
  -webkit-backdrop-filter: blur(4px); backdrop-filter: blur(4px);
}
#pin-overlay[hidden] { display: none; }
#pin-panel {
  background: var(--card); border-radius: 24px; padding: 28px; width: min(340px, 86vw); text-align: center;
}
#pin-icon { font-size: 2.4rem; }
#pin-panel h2 { margin: 6px 0 2px; }
#pin-panel p { margin: 0 0 16px; color: var(--muted); }
#pin-input {
  width: 140px; text-align: center; font-size: 2rem; letter-spacing: .4em;
  padding: 10px; border: 2px solid var(--line); border-radius: 14px; background: var(--bg);
}
#pin-error { color: #ff3b30; margin-top: 10px; font-size: .9rem; }
.pin-actions { display: flex; gap: 10px; margin-top: 20px; }
.pin-actions button { flex: 1; padding: 13px; border-radius: 13px; font-size: 1rem; font-weight: 600; }
#pin-cancel { background: var(--subtle); }
#pin-submit { background: var(--accent); color: #fff; }