:root {
  --blue: #1F4E79;
  --blue-light: #DCE6F1;
  --red-accent: #8A3324;
  --text: #2b2b2b;
  --muted: #767676;
  --border: #e2e2e2;
  --bg: #fdfcfa;
  --card-bg: #ffffff;
  --lvl-int: #FFF3CC;
  --lvl-adv: #F2D2CE;
  --lvl-root: #D9EAD3;
  --lvl-gram: #E7E7E7;
  --lvl-new: #EDEDFA;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }

html, body {
  margin: 0; padding: 0;
  font-family: var(--sans);
  color: var(--text);
  background: var(--bg);
  line-height: 1.6;
}

a { color: var(--blue); text-decoration: none; }
a:hover { text-decoration: underline; }

.app-header {
  position: sticky; top: 0; z-index: 20;
  display: flex; align-items: center; justify-content: space-between;
  padding: 10px 18px;
  background: var(--blue);
  color: white;
  box-shadow: 0 1px 6px rgba(0,0,0,0.15);
}
.app-header .brand { display: flex; align-items: baseline; gap: 10px; cursor: pointer; }
.app-header .brand .brand-mira { font-weight: 700; font-size: 1.15rem; letter-spacing: 0.3px; }
.app-header .brand .brand-sub { font-size: 0.78rem; opacity: 0.85; }
.app-header .header-actions { display: flex; align-items: center; gap: 10px; }
.menu-toggle { display: none; background: none; border: 1px solid rgba(255,255,255,0.5); color: white; border-radius: 6px; padding: 5px 10px; cursor: pointer; font-size: 1rem; }

.lang-toggle {
  background: rgba(255,255,255,0.12);
  border: 1px solid rgba(255,255,255,0.5);
  color: white;
  border-radius: 20px;
  padding: 5px 14px;
  font-size: 0.85rem;
  cursor: pointer;
  font-weight: 600;
  letter-spacing: 0.5px;
}
.lang-toggle:hover { background: rgba(255,255,255,0.22); }

.layout { display: flex; max-width: 1180px; margin: 0 auto; min-height: calc(100vh - 52px); }

.sidebar {
  width: 260px; flex: 0 0 260px;
  border-right: 1px solid var(--border);
  padding: 16px 12px 40px;
  background: #faf9f6;
}
.sidebar nav a.top-link {
  display: block; padding: 7px 10px; border-radius: 6px; font-size: 0.9rem; color: var(--text);
  margin-bottom: 2px;
}
.sidebar nav a.top-link:hover { background: var(--blue-light); text-decoration: none; }
.sidebar nav a.top-link.active { background: var(--blue); color: white; }

.sidebar .chapter-block { margin-top: 14px; }
.sidebar .chapter-title {
  font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.5px;
  color: var(--muted); font-weight: 700; padding: 4px 10px; margin-top: 4px;
}
.sidebar .lesson-link {
  display: block; padding: 5px 10px 5px 18px; border-radius: 6px; font-size: 0.86rem;
  color: var(--text); margin-bottom: 1px;
}
.sidebar .lesson-link:hover { background: var(--blue-light); text-decoration: none; }
.sidebar .lesson-link.active { background: var(--blue); color: white; font-weight: 600; }

.main-content { flex: 1; min-width: 0; padding: 26px 32px 60px; }

.cover-block { text-align: center; padding: 30px 10px 20px; }
.cover-block h1 { color: var(--blue); font-size: 2.1rem; margin-bottom: 6px; }
.cover-block .sub { color: var(--muted); font-size: 1.05rem; margin-bottom: 4px; }

.prose p { margin: 0 0 12px; }
.prose { max-width: 760px; }

.section-card {
  background: var(--card-bg); border: 1px solid var(--border); border-radius: 10px;
  padding: 18px 22px; margin-bottom: 22px;
}
.section-card h2 {
  color: var(--blue); font-size: 1.15rem; margin: 0 0 14px;
  border-bottom: 2px solid var(--blue-light); padding-bottom: 8px;
}
.section-card h3 { color: var(--blue); font-size: 1rem; margin: 16px 0 8px; }

.chapter-intro-list { display: flex; flex-direction: column; gap: 14px; margin-top: 10px; }
.chapter-intro-card {
  border: 1px solid var(--border); border-radius: 10px; padding: 16px 18px; background: var(--card-bg);
  transition: box-shadow 0.15s; display: block;
}
.chapter-intro-card:hover { box-shadow: 0 2px 10px rgba(0,0,0,0.08); text-decoration: none; }
.chapter-intro-card .ci-title { color: var(--blue); font-weight: 700; margin-bottom: 4px; }
.chapter-intro-card .ci-desc { color: #555; font-size: 0.92rem; margin-bottom: 6px; }
.chapter-intro-card .ci-lessons { color: var(--muted); font-size: 0.8rem; }

.lesson-header { margin-bottom: 4px; }
.lesson-header h1 { color: var(--blue); margin: 0 0 4px; font-size: 1.6rem; }
.lesson-header .unit-note { color: var(--muted); font-size: 0.85rem; font-style: italic; margin-bottom: 18px; }

table.data-table { width: 100%; border-collapse: collapse; font-size: 0.92rem; }
table.data-table th, table.data-table td {
  border: 1px solid var(--border); padding: 7px 10px; text-align: left; vertical-align: top;
}
table.data-table th { background: var(--blue-light); color: var(--blue); font-weight: 700; }
table.data-table tr:nth-child(even) td { background: #faf9f6; }

.dialogue-row .speaker { font-weight: 700; color: var(--red-accent); width: 30px; }
.dialogue-row .mira { font-weight: 700; color: var(--blue); }
.dialogue-row .gloss { color: #444; }

.vocab-word { font-weight: 700; color: var(--blue); }
.vocab-en { color: #666; font-style: italic; }
.level-pill { display: inline-block; padding: 1px 8px; border-radius: 10px; font-size: 0.78rem; font-weight: 600; }
.level-int { background: var(--lvl-int); } .level-adv { background: var(--lvl-adv); }
.level-root { background: var(--lvl-root); } .level-gram { background: var(--lvl-gram); }
.level-new { background: var(--lvl-new); } .level-beg { background: transparent; color: var(--muted); }

.pattern-line { margin: 0 0 10px; }
.pattern-line .p-nova { color: var(--blue); font-weight: 700; }
.pattern-line .p-gloss { color: #444; margin-left: 6px; }

.grammar-para { margin: 0 0 12px; color: #333; }

.exercise-item { margin-bottom: 14px; border-bottom: 1px dashed var(--border); padding-bottom: 12px; }
.exercise-item:last-child { border-bottom: none; }
.exercise-tag { font-weight: 700; color: var(--blue); margin-right: 6px; }
.exercise-prompt { font-weight: 500; }
.exercise-prompt .nova-highlight { color: var(--blue); font-weight: 700; }
.reveal-btn {
  display: inline-block; margin-top: 6px; font-size: 0.82rem; color: var(--blue);
  cursor: pointer; user-select: none; border: 1px dashed var(--blue); border-radius: 5px; padding: 2px 8px;
}
.exercise-answer { margin-top: 6px; padding: 8px 12px; background: #f4f7fa; border-left: 3px solid var(--blue); border-radius: 4px; display: none; font-size: 0.92rem; }
.exercise-answer.shown { display: block; }
.exercise-answer .ans-note { color: #666; font-size: 0.85rem; margin-top: 3px; }

.summary-list { margin: 0; padding-left: 20px; }
.summary-list li { margin-bottom: 6px; }

.lesson-nav { display: flex; justify-content: space-between; margin: 30px 0 10px; gap: 10px; }
.lesson-nav a { padding: 8px 16px; border: 1px solid var(--blue); border-radius: 6px; color: var(--blue); font-size: 0.9rem; }
.lesson-nav a:hover { background: var(--blue-light); text-decoration: none; }
.lesson-nav .spacer { flex: 1; }

.footer-note { text-align: center; color: var(--muted); font-size: 0.8rem; margin-top: 40px; padding-top: 16px; border-top: 1px solid var(--border); }

.level-note-text { color: var(--muted); font-size: 0.8rem; margin-top: 8px; }

.resource-list, .toc-list { padding-left: 20px; }
.resource-list li, .toc-list li { margin-bottom: 8px; }

.search-box { margin: 10px 0 18px; }
.search-box input {
  width: 100%; padding: 8px 12px; border: 1px solid var(--border); border-radius: 6px; font-size: 0.9rem;
}

@media (max-width: 860px) {
  .menu-toggle { display: inline-block; }
  .layout { flex-direction: column; }
  .sidebar {
    width: 100%; flex: none; display: none; border-right: none; border-bottom: 1px solid var(--border);
    max-height: 60vh; overflow-y: auto;
  }
  .sidebar.open { display: block; }
  .main-content { padding: 18px 16px 50px; }
}