* { margin: 0; padding: 0; box-sizing: border-box; }

:root {
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "PingFang TC", "Microsoft JhengHei", sans-serif;
  --color-bg: #ffffff;
  --color-surface: #f8f8f8;
  --color-text: #000000;
  --color-text-secondary: #666666;
  --color-border: #e0e0e0;
  --color-accent: #1976d2;
  --hat-white: #b0b0b0;
  --hat-red: #ff5252;
  --hat-black: #3a4a4b;
  --hat-yellow: #ffcc00;
  --hat-green: #4caf50;
  --hat-blue: #42a5f5;
  --max-width: 900px;
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  line-height: 1.35;
  height: 100vh;
  display: flex;
  flex-direction: column;
  font-size: 16px;
  background: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

input, button, select, textarea {
  font-family: inherit;
}

header {
  flex-shrink: 0;
  display: flex;
  align-items: stretch;
  padding: 4px 16px 4px 8px;
  border-bottom: 1px solid var(--color-border);
}

.header-search-container {
  flex: 1;
  position: relative;
  display: flex;
  align-items: stretch;
}

.header-search {
  width: 100%;
  padding: 0 var(--space-2);
  border: 1px solid var(--color-border);
  border-radius: 0;
  background: var(--color-surface);
  font: inherit;
  font-size: 14px;
  line-height: 1.2;
}

.header-search:focus {
  outline: none;
  border-color: var(--color-text);
  background: var(--color-bg);
}

.header-search-dropdown {
  display: none;
  position: absolute;
  top: calc(100% + var(--space-1));
  left: 0;
  right: 0;
  max-height: min(70vh, 520px);
  overflow-y: auto;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
  z-index: 1000;
}

.header-search-dropdown.active { display: block; }

.header-search-dropdown a {
  display: block;
  padding: var(--space-2);
  border-bottom: 1px solid var(--color-border);
  text-decoration: none;
  color: var(--color-text);
  font-size: 14px;
}

.header-search-dropdown a:last-child { border-bottom: none; }
.header-search-dropdown a:hover { background: var(--color-surface); }

.search-group-label {
  padding: 6px 12px;
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--color-text-secondary);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
}

.search-meta {
  float: right;
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-size: 10px;
  color: var(--color-text-secondary);
}

.level-pill {
  display: inline-block;
  font-size: 9px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 1px 5px;
  border: 1px solid var(--color-border);
}

.level-pill.sl { background: #e3f2fd; color: #1565c0; border-color: #bbdefb; }
.level-pill.hl { background: #fce4ec; color: #c2185b; border-color: #f8bbd0; }

main {
  flex: 1;
  overflow-y: auto;
  padding: var(--space-1) var(--space-4) var(--space-3);
}

.container {
  max-width: var(--max-width);
  margin: 0 auto;
}

.empty-state {
  color: var(--color-text-secondary);
  font-size: 15px;
  line-height: 1.4;
}

.empty-state p { margin-bottom: var(--space-2); }
.empty-hint { font-size: 14px; }

.main-topic-title {
  font-size: 22px;
  font-weight: 600;
  margin-bottom: var(--space-2);
  letter-spacing: -0.02em;
  cursor: pointer;
}

.main-topic-title:hover { opacity: 0.75; }

.topic-prefix { font-weight: 400; }

.topic-meta {
  font-size: 13px;
  color: var(--color-text-secondary);
  margin-bottom: var(--space-1);
}

.level-tag {
  display: inline-block;
  font-size: 10px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 1px 6px;
  margin-left: 6px;
  border: 1px solid var(--color-border);
}

.level-tag.sl { background: #e3f2fd; color: #1565c0; }
.level-tag.hl { background: #fce4ec; color: #c2185b; }
.level-tag.both { background: #f3e5f5; color: #6a1b9a; }

.session-dropdown {
  margin-bottom: var(--space-2);
  padding: 6px 10px;
  font: inherit;
  border: 1px solid var(--color-border);
}

.topic-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: var(--space-2);
}

.topic-actions span,
.topic-actions a {
  font-size: 14px;
  cursor: pointer;
  color: var(--color-text);
  text-decoration: underline;
}

.vocab-list { margin-bottom: var(--space-2); }

.vocab-items {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1);
  align-items: center;
}

.vocab-list-title {
  font-size: 13px;
  font-weight: 500;
  color: var(--color-text-secondary);
}

.vocab-exercise-link {
  cursor: pointer;
  text-decoration: underline;
  color: var(--color-text);
}

.article-exercise-prompt {
  margin-top: 14px;
  margin-bottom: 0;
  padding-top: 12px;
  border-top: 1px solid var(--color-border);
  font-size: 14px;
}

.vocab-item {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 2px 8px;
  border: 1px solid var(--color-border);
  cursor: pointer;
  font-size: 14px;
}

.vocab-translation {
  display: none;
  color: var(--color-text-secondary);
  font-size: 13px;
}

.vocab-item.revealed .vocab-translation {
  display: inline;
  color: #333;
}

.article-text {
  display: none;
  margin: var(--space-2) 0;
  padding: var(--space-2);
  border: 1px solid var(--color-border);
  line-height: 1.5;
}

.article-text.show { display: block; }
.article-text p { margin-bottom: 10px; }
.article-text ul { margin: 8px 0 8px 20px; }

.questions { margin-top: var(--space-1); }

.question {
  padding: var(--space-1) var(--space-2);
  cursor: pointer;
  border-left: 3px solid transparent;
  transition: background 0.15s;
}

.question:hover { background: var(--color-surface); }

.question.revealed.white-hat { border-left-color: var(--hat-white); background: rgba(176,176,176,0.12); }
.question.revealed.red-hat { border-left-color: var(--hat-red); background: rgba(255,82,82,0.15); }
.question.revealed.black-hat { border-left-color: var(--hat-black); background: rgba(58,74,75,0.15); }
.question.revealed.yellow-hat { border-left-color: var(--hat-yellow); background: rgba(255,204,0,0.15); }
.question.revealed.green-hat { border-left-color: var(--hat-green); background: rgba(76,175,80,0.15); }
.question.revealed.blue-hat { border-left-color: var(--hat-blue); background: rgba(66,165,245,0.15); }

.question-emoji, .question-label { display: none; }
.question.revealed .question-emoji { display: inline; margin-right: var(--space-1); }
.question.revealed .question-label {
  display: inline;
  font-size: 10px;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-left: var(--space-2);
  font-weight: 600;
}

.loading { padding: var(--space-4); color: var(--color-text-secondary); }

.help-button {
  position: fixed;
  bottom: 16px;
  right: 16px;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--color-border);
  border-radius: 50%;
  background: var(--color-bg);
  color: var(--color-text-secondary);
  text-decoration: none;
  font-size: 16px;
  font-weight: 600;
  line-height: 1;
  z-index: 50;
}

.help-button:hover {
  background: var(--color-surface);
  color: var(--color-text);
}

.vocab-exercise-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.4);
  z-index: 200;
  align-items: center;
  justify-content: center;
  padding: 16px;
}

.vocab-exercise-overlay.open { display: flex; }

.vocab-exercise-modal {
  background: var(--color-bg);
  max-width: 640px;
  width: 100%;
  max-height: 90vh;
  overflow-y: auto;
  padding: var(--space-3);
  position: relative;
  border: 1px solid var(--color-border);
}

.vocab-exercise-close {
  position: absolute;
  top: 8px;
  right: 12px;
  border: none;
  background: none;
  font-size: 24px;
  cursor: pointer;
}

.vocab-exercise-keywords {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 16px;
}

.vocab-exercise-keyword {
  padding: 6px 12px;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  cursor: pointer;
  font-size: 14px;
}

.vocab-exercise-keyword.selected {
  border-color: var(--color-text);
  background: var(--color-bg);
}

.vocab-blank {
  display: inline-block;
  min-width: 80px;
  padding: 0 4px;
  border-bottom: 2px solid var(--color-text-secondary);
  cursor: pointer;
}

.vocab-blank.correct { background: rgba(76,175,80,0.15); border-color: var(--hat-green); }
.vocab-blank.incorrect { background: rgba(244,67,54,0.15); border-color: var(--hat-red); }

@media (max-width: 600px) {
  header { padding: 4px 8px; }
}