:root {
  --bb-blue: #0d2a4f;
  --bb-accent: #1a73e8;
  --bb-bg: #f4f5f7;
  --bb-card: #ffffff;
  --bb-border: #d6d9de;
  --bb-text: #1f2933;
  --bb-flag: #d93025;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body {
  font-family: -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bb-bg); color: var(--bb-text);
}
#app { max-width: 880px; margin: 0 auto; min-height: 100vh; display: flex; flex-direction: column; }

/* ---------- top bar ---------- */
.topbar {
  background: var(--bb-blue); color: #fff; padding: 10px 20px;
  display: flex; align-items: center; justify-content: space-between;
  border-radius: 0 0 8px 8px;
}
.topbar .title { font-weight: 600; font-size: 15px; }
.timer { font-variant-numeric: tabular-nums; font-size: 17px; display: flex; gap: 8px; align-items: center; }
.timer.warn { color: #ff8a80; font-weight: 700; }
.timer button { background: none; border: 1px solid #ffffff66; color: #fff; border-radius: 4px; padding: 2px 8px; cursor: pointer; font-size: 12px; }

/* ---------- start / submit / result screens ---------- */
.center-card {
  background: var(--bb-card); border: 1px solid var(--bb-border); border-radius: 10px;
  padding: 36px; margin: 60px 20px; text-align: center;
}
.center-card h1 { font-size: 22px; margin-bottom: 14px; color: var(--bb-blue); }
.center-card p { margin: 8px 0; line-height: 1.6; }
.big-btn {
  background: var(--bb-accent); color: #fff; border: none; border-radius: 6px;
  padding: 12px 36px; font-size: 16px; cursor: pointer; margin-top: 20px;
}
.big-btn:hover { filter: brightness(1.1); }
.big-btn:disabled { background: #9db8dd; cursor: wait; }
.summary-list { text-align: left; display: inline-block; margin: 12px 0; }

/* ---------- question ---------- */
.qwrap { flex: 1; padding: 20px; }
.qhead { display: flex; justify-content: space-between; align-items: center; margin-bottom: 12px; }
.qnum { font-size: 13px; color: #667; background: #e8ebef; padding: 3px 10px; border-radius: 12px; }
.flag-btn { background: none; border: 1px solid var(--bb-border); border-radius: 6px; padding: 4px 10px; cursor: pointer; font-size: 13px; color: #667; }
.flag-btn.flagged { color: var(--bb-flag); border-color: var(--bb-flag); font-weight: 700; }
.stem-card {
  background: var(--bb-card); border: 1px solid var(--bb-border); border-radius: 10px;
  padding: 24px; font-size: 17px; line-height: 1.75; margin-bottom: 18px; white-space: pre-wrap;
}
.stem-card .blank { font-weight: 700; color: var(--bb-accent); letter-spacing: 2px; }
.stem-card mark { background: #ffe58f; padding: 0 1px; border-radius: 2px; }
.question-line { font-size: 14px; color: #556; font-style: italic; margin-bottom: 12px; }

.choice {
  display: flex; align-items: flex-start; gap: 12px;
  background: var(--bb-card); border: 1.5px solid var(--bb-border); border-radius: 8px;
  padding: 13px 16px; margin-bottom: 10px; cursor: pointer;
}
.choice:hover { border-color: var(--bb-accent); }
.choice.selected { border-color: var(--bb-accent); background: #eaf2fe; }
.choice .letter {
  flex: none; width: 26px; height: 26px; border: 1.5px solid var(--bb-accent); border-radius: 50%;
  display: flex; align-items: center; justify-content: center; font-weight: 700; color: var(--bb-accent); font-size: 14px;
}
.choice.selected .letter { background: var(--bb-accent); color: #fff; }
.choice .text { flex: 1; font-size: 16px; line-height: 1.5; }
.choice .text.struck { text-decoration: line-through; color: #99a; }
.elim-btn {
  flex: none; background: none; border: 1px solid var(--bb-border); border-radius: 4px;
  font-size: 11px; color: #889; padding: 3px 6px; cursor: pointer;
}
.elim-btn.on { color: var(--bb-flag); border-color: var(--bb-flag); }

/* ---------- bottom bar ---------- */
.bottombar {
  display: flex; justify-content: space-between; align-items: center;
  background: var(--bb-card); border-top: 1px solid var(--bb-border);
  padding: 12px 20px; border-radius: 8px 8px 0 0;
}
.nav-btn {
  background: var(--bb-blue); color: #fff; border: none; border-radius: 6px;
  padding: 9px 26px; font-size: 15px; cursor: pointer;
}
.nav-btn:disabled { background: #b9c2cd; cursor: not-allowed; }
.qpos { background: none; border: none; color: var(--bb-accent); font-size: 14px; cursor: pointer; text-decoration: underline; }

/* ---------- navigator grid ---------- */
.overlay { position: fixed; inset: 0; background: rgba(0,0,0,.45); display: flex; align-items: center; justify-content: center; z-index: 10; }
.nav-panel { background: #fff; border-radius: 12px; padding: 28px; width: min(480px, 92vw); }
.nav-panel h2 { font-size: 17px; margin-bottom: 6px; color: var(--bb-blue); }
.nav-panel .legend { font-size: 12px; color: #778; margin-bottom: 14px; }
.grid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 10px; margin-bottom: 18px; }
.cell {
  position: relative; aspect-ratio: 1; border: 1.5px solid var(--bb-border); border-radius: 8px;
  display: flex; align-items: center; justify-content: center; font-size: 15px; cursor: pointer; background: #fff;
}
.cell.answered { background: var(--bb-blue); color: #fff; border-color: var(--bb-blue); }
.cell.current { outline: 3px solid var(--bb-accent); }
.cell .dot { position: absolute; top: 3px; right: 3px; width: 9px; height: 9px; background: var(--bb-flag); border-radius: 50%; }
.close-btn { width: 100%; padding: 10px; border: 1px solid var(--bb-border); border-radius: 6px; background: #fff; cursor: pointer; font-size: 14px; }

/* ---------- results ---------- */
.result-q { background: var(--bb-card); border: 1px solid var(--bb-border); border-radius: 10px; padding: 20px 24px; margin: 14px 20px; }
.result-q h3 { font-size: 15px; margin-bottom: 8px; }
.result-q .verdict { font-weight: 700; }
.verdict.ok { color: #188038; } .verdict.bad { color: var(--bb-flag); }
.result-q .stem { font-size: 14.5px; line-height: 1.6; color: #445; margin: 8px 0; white-space: pre-wrap; }
.result-q .ex { font-size: 14px; line-height: 1.6; background: #f6f8fa; border-radius: 6px; padding: 12px; margin-top: 8px; white-space: pre-wrap; }
.result-q .pick { font-size: 14px; margin: 4px 0; }
.score-line { font-size: 20px; font-weight: 700; color: var(--bb-blue); }