:root {
  --primary: #1b7a43;
  --primary-dark: #0b3d2e;
  --primary-light: #2e9c5c;
  --accent: #f2a71b;
  --bg: #f3f6f4;
  --card-bg: #ffffff;
  --text: #1a2420;
  --muted: #6b7c74;
  --border: #e1e8e4;
  --danger: #c0392b;
  --danger-bg: #fdecea;
  --warn: #b7791f;
  --warn-bg: #fef6e6;
  --good: #16794a;
  --good-bg: #e8f7ee;
  --radius: 14px;
  --shadow: 0 2px 10px rgba(11, 61, 46, 0.08);
  --safe-top: env(safe-area-inset-top, 0px);
  --safe-bottom: env(safe-area-inset-bottom, 0px);
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  background: var(--bg);
  color: var(--text);
  font-family: "Segoe UI", Roboto, -apple-system, BlinkMacSystemFont, Helvetica, Arial, sans-serif;
  -webkit-tap-highlight-color: transparent;
}

#app {
  max-width: 560px;
  margin: 0 auto;
  min-height: 100%;
  display: flex;
  flex-direction: column;
  background: var(--bg);
  position: relative;
  padding-bottom: calc(72px + var(--safe-bottom));
}

/* ---------- Install banner ---------- */
#install-banner {
  display: none;
  align-items: center;
  gap: 10px;
  background: linear-gradient(135deg, var(--primary), var(--primary-light));
  color: #fff;
  padding: calc(10px + var(--safe-top)) 14px 10px 14px;
  position: sticky;
  top: 0;
  z-index: 50;
  box-shadow: 0 2px 8px rgba(0,0,0,0.15);
}
#install-banner.show { display: flex; }
#install-banner .ib-icon { font-size: 20px; flex-shrink: 0; }
#install-banner .ib-text { flex: 1; font-size: 13px; line-height: 1.3; }
#install-banner .ib-text strong { display: block; font-size: 14px; }
#install-banner button {
  border: none;
  border-radius: 8px;
  padding: 8px 12px;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
}
#install-banner .ib-install {
  background: #fff;
  color: var(--primary-dark);
}
#install-banner .ib-dismiss {
  background: transparent;
  color: #fff;
  font-size: 18px;
  padding: 4px 8px;
  opacity: 0.85;
}

/* ---------- Header ---------- */
header.app-header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 16px;
  background: var(--card-bg);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 40;
}
header.app-header img.logo {
  height: 42px;
  width: auto;
  object-fit: contain;
}
header.app-header .htitles { flex: 1; min-width: 0; }
header.app-header .htitles h1 {
  font-size: 17px;
  margin: 0;
  color: var(--primary-dark);
  line-height: 1.2;
}
header.app-header .htitles p {
  font-size: 11.5px;
  margin: 2px 0 0;
  color: var(--muted);
}
header.app-header .back-btn {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  width: 38px;
  height: 38px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  color: var(--primary-dark);
  cursor: pointer;
  flex-shrink: 0;
}

/* ---------- Main content ---------- */
main {
  flex: 1;
  padding: 16px;
}

.section-title {
  font-size: 15px;
  font-weight: 700;
  color: var(--primary-dark);
  margin: 4px 0 12px;
}
.section-sub {
  font-size: 13px;
  color: var(--muted);
  margin: -8px 0 16px;
}

/* ---------- Unit cards (home) ---------- */
.unit-grid {
  display: flex;
  flex-direction: column;
  gap: 14px;
}
.unit-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
  display: flex;
  align-items: center;
  gap: 14px;
  cursor: pointer;
  border: 1px solid var(--border);
  transition: transform .12s ease;
}
.unit-card:active { transform: scale(0.98); }
.unit-card .unit-icon {
  width: 54px;
  height: 54px;
  border-radius: 14px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 26px;
  color: #fff;
  flex-shrink: 0;
}
.unit-card:nth-child(1) .unit-icon { background: linear-gradient(135deg,#1b7a43,#2e9c5c); }
.unit-card:nth-child(2) .unit-icon { background: linear-gradient(135deg,#146b8c,#1f9bc7); }
.unit-card:nth-child(3) .unit-icon { background: linear-gradient(135deg,#8c3f14,#c76a25); }
.unit-card .unit-info { flex: 1; min-width: 0; }
.unit-card .unit-info h2 { font-size: 15px; margin: 0 0 2px; color: var(--text); }
.unit-card .unit-info p { font-size: 12.5px; margin: 0 0 6px; color: var(--muted); line-height: 1.35; }
.unit-card .unit-progress-bar {
  height: 6px;
  border-radius: 4px;
  background: var(--border);
  overflow: hidden;
}
.unit-card .unit-progress-bar > div {
  height: 100%;
  background: var(--primary);
  border-radius: 4px;
}
.unit-card .chevron { color: var(--muted); font-size: 18px; flex-shrink: 0; }

/* ---------- Topic list ---------- */
.topic-list { display: flex; flex-direction: column; gap: 10px; }
.topic-item {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px;
  display: flex;
  align-items: center;
  gap: 12px;
  cursor: pointer;
}
.topic-item:active { transform: scale(0.99); }
.topic-item .t-num {
  width: 30px; height: 30px;
  border-radius: 50%;
  background: var(--bg);
  color: var(--primary-dark);
  font-size: 12px;
  font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0;
  border: 1px solid var(--border);
}
.topic-item .t-info { flex: 1; min-width: 0; }
.topic-item .t-info h3 { font-size: 13.5px; margin: 0 0 4px; line-height: 1.3; color: var(--text); }
.badge {
  display: inline-block;
  font-size: 10.5px;
  font-weight: 700;
  padding: 3px 8px;
  border-radius: 20px;
  letter-spacing: .2px;
}
.badge.not-started { background: var(--bg); color: var(--muted); border: 1px solid var(--border); }
.badge.mastered { background: var(--good-bg); color: var(--good); }
.badge.reviewed { background: #e7f1fb; color: #1d5f96; }
.badge.reinforce { background: var(--danger-bg); color: var(--danger); }
.topic-item .chevron { color: var(--muted); font-size: 16px; }

/* ---------- Topic detail ---------- */
.topic-detail .concepts {
  background: var(--card-bg);
  border-radius: var(--radius);
  border: 1px solid var(--border);
  padding: 18px;
  font-size: 14px;
  line-height: 1.65;
  box-shadow: var(--shadow);
}
.topic-detail .concepts h1 {
  font-size: 18px;
  color: var(--primary-dark);
  margin: 0 0 12px;
}
.topic-detail .concepts p { margin: 0 0 12px; }
.topic-detail .concepts ul { margin: 0 0 12px; padding-left: 20px; }
.topic-detail .concepts li { margin-bottom: 8px; }
.topic-detail .concepts strong { color: var(--primary-dark); }

.cta-quiz {
  margin-top: 16px;
  width: 100%;
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: 12px;
  padding: 14px;
  font-size: 15px;
  font-weight: 700;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  box-shadow: var(--shadow);
}
.cta-quiz:active { transform: scale(0.98); }
.last-result-note {
  margin-top: 10px;
  font-size: 12.5px;
  color: var(--muted);
  text-align: center;
}

/* ---------- Quiz ---------- */
.quiz-progress {
  display: flex;
  gap: 6px;
  margin-bottom: 16px;
}
.quiz-progress > div {
  flex: 1;
  height: 5px;
  border-radius: 4px;
  background: var(--border);
}
.quiz-progress > div.done { background: var(--primary); }
.quiz-progress > div.current { background: var(--primary-light); }

.quiz-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
  box-shadow: var(--shadow);
}
.quiz-card .q-count {
  font-size: 12px;
  color: var(--muted);
  font-weight: 600;
  margin-bottom: 6px;
}
.quiz-card h2 {
  font-size: 15.5px;
  margin: 0 0 16px;
  line-height: 1.4;
  color: var(--text);
}
.quiz-options { display: flex; flex-direction: column; gap: 10px; }
.quiz-option {
  border: 1.5px solid var(--border);
  border-radius: 10px;
  padding: 12px 14px;
  font-size: 13.5px;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 10px;
  background: var(--bg);
}
.quiz-option .opt-letter {
  width: 24px; height: 24px;
  border-radius: 50%;
  background: #fff;
  border: 1.5px solid var(--border);
  font-size: 11.5px;
  font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0;
  color: var(--muted);
}
.quiz-option.selected { border-color: var(--primary); background: #eaf6ee; }
.quiz-option.selected .opt-letter { background: var(--primary); border-color: var(--primary); color: #fff; }
.quiz-option.correct { border-color: var(--good); background: var(--good-bg); }
.quiz-option.correct .opt-letter { background: var(--good); border-color: var(--good); color: #fff; }
.quiz-option.incorrect { border-color: var(--danger); background: var(--danger-bg); }
.quiz-option.incorrect .opt-letter { background: var(--danger); border-color: var(--danger); color: #fff; }
.quiz-option.disabled { cursor: default; }

.quiz-explain {
  margin-top: 14px;
  padding: 12px 14px;
  background: var(--bg);
  border-radius: 10px;
  font-size: 12.5px;
  color: var(--muted);
  line-height: 1.5;
  border-left: 3px solid var(--primary);
}

.quiz-nav {
  display: flex;
  gap: 10px;
  margin-top: 16px;
}
.quiz-nav button {
  flex: 1;
  padding: 13px;
  border-radius: 12px;
  border: none;
  font-size: 14px;
  font-weight: 700;
  cursor: pointer;
}
.btn-primary { background: var(--primary); color: #fff; }
.btn-secondary { background: var(--card-bg); color: var(--primary-dark); border: 1.5px solid var(--border) !important; }
.btn-primary:disabled { background: #b9d9c4; cursor: not-allowed; }

/* ---------- Quiz results ---------- */
.result-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px 18px;
  text-align: center;
  box-shadow: var(--shadow);
}
.result-score {
  font-size: 42px;
  font-weight: 800;
  margin: 6px 0;
}
.result-score.mastered { color: var(--good); }
.result-score.reviewed { color: #1d5f96; }
.result-score.reinforce { color: var(--danger); }
.result-label { font-size: 14px; font-weight: 700; margin-bottom: 4px; }
.result-sub { font-size: 12.5px; color: var(--muted); margin-bottom: 18px; }
.result-actions { display: flex; gap: 10px; margin-top: 6px; }
.result-actions button { flex: 1; padding: 13px; border-radius: 12px; border: none; font-weight: 700; font-size: 13.5px; cursor: pointer; }

.review-list { margin-top: 18px; text-align: left; display: flex; flex-direction: column; gap: 12px; }
.review-item { border-radius: 10px; padding: 12px; font-size: 12.5px; border: 1px solid var(--border); }
.review-item.ok { background: var(--good-bg); }
.review-item.bad { background: var(--danger-bg); }
.review-item .rq { font-weight: 700; margin-bottom: 6px; }
.review-item .ra { color: var(--muted); }

/* ---------- Progress / Summary screen ---------- */
.progress-summary-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin-bottom: 20px;
}
.stat-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px 8px;
  text-align: center;
}
.stat-card .num { font-size: 22px; font-weight: 800; }
.stat-card .lab { font-size: 10.5px; color: var(--muted); margin-top: 2px; }
.stat-card.mastered .num { color: var(--good); }
.stat-card.reviewed .num { color: #1d5f96; }
.stat-card.reinforce .num { color: var(--danger); }

.summary-block { margin-bottom: 20px; }
.summary-block h3 {
  font-size: 13.5px;
  color: var(--primary-dark);
  margin: 0 0 10px;
  display: flex;
  align-items: center;
  gap: 6px;
}
.summary-topic-row {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 11px 13px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  margin-bottom: 8px;
  cursor: pointer;
}
.summary-topic-row .stt { font-size: 12.5px; flex: 1; }
.summary-topic-row .stu { font-size: 10px; color: var(--muted); display: block; margin-top: 2px; }
.summary-topic-row .stp { font-size: 12.5px; font-weight: 800; flex-shrink: 0; }
.empty-note {
  font-size: 12.5px;
  color: var(--muted);
  background: var(--card-bg);
  border: 1px dashed var(--border);
  border-radius: 10px;
  padding: 14px;
  text-align: center;
}

/* ---------- Bottom nav ---------- */
nav.bottom-nav {
  position: fixed;
  bottom: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 100%;
  max-width: 560px;
  background: var(--card-bg);
  border-top: 1px solid var(--border);
  display: flex;
  padding-bottom: var(--safe-bottom);
  z-index: 45;
}
nav.bottom-nav button {
  flex: 1;
  border: none;
  background: transparent;
  padding: 10px 4px 8px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 3px;
  font-size: 10.5px;
  color: var(--muted);
  cursor: pointer;
}
nav.bottom-nav button .nav-icon { font-size: 19px; }
nav.bottom-nav button.active { color: var(--primary); font-weight: 700; }

/* ---------- Utility ---------- */
.hidden { display: none !important; }
.fade-in { animation: fadeIn .18s ease; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(4px);} to { opacity: 1; transform: translateY(0);} }

.loading-note { text-align:center; padding: 40px 20px; color: var(--muted); font-size: 13px; }

footer.app-footer {
  text-align: center;
  font-size: 10.5px;
  color: var(--muted);
  padding: 18px 16px 4px;
}