/* ============================================
   RootWords — Nordic Minimalist Design System
   ============================================ */

/* --- CSS Variables (Nordic Palette) --- */
:root {
  --color-bg:         #F5F0EB;   /* 暖白 — 主背景 */
  --color-surface:    #FFFFFF;   /* 纯白 — 卡片背景 */
  --color-text:       #2C3E50;   /* 深蓝灰 — 主文字 */
  --color-text-soft:  #7B8D9E;   /* 柔灰蓝 — 次要文字 */
  --color-text-muted: #B0BEC5;   /* 浅灰蓝 — 辅助文字 */
  --color-border:     #E8E0D8;   /* 暖灰 — 分割线 */
  --color-accent:     #7FA998;   /* 鼠尾草绿 — 主强调色 */
  --color-accent-alt: #D4A574;   /* 暖木色 — 次强调色 */
  --color-accent-blue:#8FADCD;   /* 雾蓝 — 第三强调色 */
  --color-highlight:  #F2E8DC;   /* 浅驼色 — 高亮背景 */
  --color-danger:     #D4847A;   /* 暖红 — 警示 */
  --color-chip-bg:    #EDE8E2;   /* 芯片背景 */

  --radius-sm: 10px;
  --radius-md: 16px;
  --radius-lg: 24px;
  --radius-xl: 32px;

  --shadow-sm: 0 1px 3px rgba(44,62,80,0.06);
  --shadow-md: 0 4px 16px rgba(44,62,80,0.08);
  --shadow-lg: 0 8px 32px rgba(44,62,80,0.10);

  --font-sans: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Inter", "Helvetica Neue", sans-serif;
  --font-serif: "Georgia", "Noto Serif SC", "Songti SC", serif;

  --safe-bottom: env(safe-area-inset-bottom, 16px);
  --header-h: 56px;
  --search-h: 72px;
  --nav-h: 52px;

  --transition: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

/* --- Reset & Base --- */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
  -webkit-tap-highlight-color: transparent;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.5;
  min-height: 100vh;
  min-height: 100dvh;
  padding-bottom: calc(var(--safe-bottom) + 24px);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

/* --- Typography --- */
h1, h2, h3, h4 {
  font-weight: 600;
  line-height: 1.25;
  letter-spacing: -0.01em;
}

/* ============================================
   Header
   ============================================ */
.header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--color-bg);
  border-bottom: 1px solid transparent;
  transition: border-color var(--transition);
}

.header.scrolled {
  border-bottom-color: var(--color-border);
  backdrop-filter: blur(12px);
  background: rgba(245,240,235,0.85);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: 720px;
  margin: 0 auto;
  padding: 12px 20px;
  height: var(--header-h);
}

.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1.25rem;
  font-weight: 650;
  letter-spacing: -0.02em;
  color: var(--color-text);
}

.logo-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 34px;
  height: 34px;
  background: var(--color-accent);
  color: #fff;
  border-radius: var(--radius-sm);
  font-size: 1.1rem;
  font-family: var(--font-serif);
}

.logo-text {
  font-family: var(--font-sans);
}

/* --- Icon Button --- */
.btn-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border: none;
  background: transparent;
  color: var(--color-text-soft);
  border-radius: 50%;
  cursor: pointer;
  transition: all var(--transition);
}

.btn-icon:hover {
  background: var(--color-chip-bg);
  color: var(--color-text);
}

.btn-icon:active {
  transform: scale(0.92);
}

/* ============================================
   Search Section
   ============================================ */
.search-section {
  z-index: 99;
  background: var(--color-bg);
  padding: 8px 20px 12px;
}

.search-container {
  position: relative;
  max-width: 680px;
  margin: 0 auto;
}

.search-box {
  display: flex;
  align-items: center;
  background: var(--color-surface);
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 12px 16px;
  transition: all var(--transition);
}

.search-box:focus-within {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-md);
}

.search-icon {
  color: var(--color-text-muted);
  flex-shrink: 0;
  transition: color var(--transition);
}

.search-box:focus-within .search-icon {
  color: var(--color-accent);
}

.search-input {
  flex: 1;
  border: none;
  outline: none;
  background: transparent;
  font-family: var(--font-sans);
  font-size: 1rem;
  color: var(--color-text);
  padding: 0 12px;
  min-width: 0;
}

.search-input::placeholder {
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

.btn-clear {
  display: none;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border: none;
  background: var(--color-chip-bg);
  color: var(--color-text-soft);
  border-radius: 50%;
  cursor: pointer;
  flex-shrink: 0;
  transition: all var(--transition);
}

.btn-clear.visible {
  display: flex;
}

.btn-clear:active {
  background: var(--color-text-muted);
  transform: scale(0.9);
}

/* --- Suggestions Dropdown --- */
.suggestions {
  display: none;
  position: absolute;
  top: calc(100% + 4px);
  left: 0;
  right: 0;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  max-height: 280px;
  overflow-y: auto;
  z-index: 10;
}

.suggestions.active {
  display: block;
}

.suggestion-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 16px;
  cursor: pointer;
  transition: background var(--transition);
  border-bottom: 1px solid var(--color-border);
}

.suggestion-item:last-child {
  border-bottom: none;
}

.suggestion-item:hover,
.suggestion-item:active {
  background: var(--color-highlight);
}

.suggestion-root {
  font-weight: 600;
  font-size: 0.95rem;
  color: var(--color-accent);
  min-width: 70px;
}

.suggestion-meaning {
  font-size: 0.85rem;
  color: var(--color-text-soft);
}

/* ============================================
   Category Navigation
   ============================================ */
.category-nav {
  z-index: 98;
  background: var(--color-bg);
  padding: 0 20px 8px;
}

.category-scroll {
  display: flex;
  gap: 8px;
  max-width: 680px;
  margin: 0 auto;
  overflow-x: auto;
  scrollbar-width: none;
  -ms-overflow-style: none;
  -webkit-overflow-scrolling: touch;
  padding-bottom: 4px;
}

.category-scroll::-webkit-scrollbar {
  display: none;
}

.chip {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  border: none;
  background: var(--color-chip-bg);
  color: var(--color-text-soft);
  border-radius: 100px;
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 500;
  cursor: pointer;
  white-space: nowrap;
  transition: all var(--transition);
  flex-shrink: 0;
  user-select: none;
}

.chip:hover {
  background: var(--color-border);
  color: var(--color-text);
}

.chip--active {
  background: var(--color-text);
  color: var(--color-bg);
}

.chip-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: currentColor;
  opacity: 0.5;
}

.chip--active .chip-dot {
  opacity: 1;
  background: var(--color-accent);
}

/* ============================================
   Main Content
   ============================================ */
.main-content {
  max-width: 720px;
  margin: 0 auto;
  padding: 16px 20px 32px;
}

/* --- Loading State --- */
.state-loading {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 80px 20px;
  color: var(--color-text-soft);
}

.spinner {
  width: 36px;
  height: 36px;
  border: 3px solid var(--color-border);
  border-top-color: var(--color-accent);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  margin-bottom: 16px;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* --- Empty State --- */
.state-empty {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 60px 20px;
  text-align: center;
}

.empty-illustration {
  margin-bottom: 20px;
  opacity: 0.6;
}

.state-empty h3 {
  font-size: 1.15rem;
  margin-bottom: 6px;
  color: var(--color-text);
}

.state-empty p {
  font-size: 0.9rem;
  color: var(--color-text-soft);
}

/* --- Roots Grid --- */
.roots-grid {
  display: flex;
  flex-direction: column;
  gap: 14px;
}

/* --- Root Card --- */
.root-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: 20px;
  cursor: pointer;
  transition: all var(--transition);
  border: 1px solid transparent;
  box-shadow: var(--shadow-sm);
  position: relative;
  overflow: hidden;
}

.root-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
}

.root-card:active {
  transform: scale(0.985);
  background: var(--color-highlight);
}

.root-card::after {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 4px;
  height: 100%;
  background: var(--card-accent, var(--color-accent));
  opacity: 0;
  transition: opacity var(--transition);
}

.root-card:hover::after {
  opacity: 1;
}

.card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 10px;
}

.card-root {
  font-family: var(--font-serif);
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--color-text);
  letter-spacing: -0.01em;
  line-height: 1.3;
}

.card-meaning {
  font-size: 0.9rem;
  color: var(--color-text-soft);
  line-height: 1.4;
}

.card-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-bottom: 12px;
}

.card-tag {
  display: inline-flex;
  align-items: center;
  padding: 3px 10px;
  border-radius: 100px;
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--color-text-soft);
  background: var(--color-chip-bg);
}

.card-tag--difficulty {
  background: var(--color-highlight);
  color: var(--color-accent-alt);
  font-weight: 600;
}

.card-preview {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.card-word-chip {
  display: inline-block;
  padding: 4px 10px;
  border-radius: 6px;
  background: var(--color-bg);
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--color-text);
  transition: all var(--transition);
}

.root-card:hover .card-word-chip {
  background: var(--color-highlight);
}

.card-count {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-size: 0.78rem;
  color: var(--color-text-muted);
  padding: 4px 10px;
}

/* ============================================
   Modal / Detail View
   ============================================ */
.modal-overlay {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 200;
  background: rgba(44,62,80,0.3);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
  padding: 20px;
  overflow-y: auto;
  align-items: flex-start;
  justify-content: center;
}

.modal-overlay.active {
  display: flex;
}

.modal {
  background: var(--color-surface);
  border-radius: var(--radius-xl);
  width: 100%;
  max-width: 560px;
  margin-top: 8vh;
  margin-bottom: 8vh;
  box-shadow: var(--shadow-lg);
  animation: modalIn 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  overflow: hidden;
}

.modal--small {
  max-width: 420px;
}

@keyframes modalIn {
  from {
    opacity: 0;
    transform: translateY(16px) scale(0.97);
  }
  to {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 20px 0;
}

.modal-title {
  font-size: 1.15rem;
  font-weight: 650;
  color: var(--color-text);
}

.modal-root-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 16px;
  background: var(--color-bg);
  border-radius: var(--radius-md);
}

.modal-root-badge .root-name {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--color-text);
}

.modal-root-badge .root-mean {
  font-size: 0.85rem;
  color: var(--color-text-soft);
}

.btn-modal-close {
  flex-shrink: 0;
}

.modal-body {
  padding: 20px;
}

/* --- Detail Section --- */
.detail-section {
  margin-bottom: 24px;
}

.detail-section:last-child {
  margin-bottom: 0;
}

.detail-section-title {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-text-soft);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 12px;
}

.detail-section-title::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--color-border);
}

/* --- Word List Item --- */
.word-item {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 14px 16px;
  background: var(--color-bg);
  border-radius: var(--radius-md);
  margin-bottom: 8px;
  transition: background var(--transition);
}

.word-item:last-child {
  margin-bottom: 0;
}

.word-item:hover {
  background: var(--color-highlight);
}

.word-main {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.word-name {
  font-size: 1.05rem;
  font-weight: 650;
  color: var(--color-text);
  letter-spacing: -0.01em;
}

.word-meaning {
  font-size: 0.9rem;
  color: var(--color-text-soft);
  text-align: right;
}

.word-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  font-size: 0.78rem;
  color: var(--color-text-muted);
}

.word-meta span {
  display: inline-flex;
  align-items: center;
  gap: 3px;
}

.word-meta .prefix-tag {
  color: var(--color-accent);
  font-weight: 500;
}

.word-meta .suffix-tag {
  color: var(--color-accent-blue);
  font-weight: 500;
}

.word-example {
  font-size: 0.83rem;
  color: var(--color-text-soft);
  font-style: italic;
  padding: 8px 12px;
  background: var(--color-surface);
  border-radius: var(--radius-sm);
  margin-top: 6px;
  border-left: 3px solid var(--color-accent);
}

/* --- About Modal --- */
.about-desc {
  font-size: 0.9rem;
  color: var(--color-text-soft);
  line-height: 1.6;
  margin-bottom: 10px;
}

.about-stats {
  display: flex;
  gap: 16px;
  padding: 16px 0;
  margin: 12px 0;
  border-top: 1px solid var(--color-border);
  border-bottom: 1px solid var(--color-border);
}

.about-stat {
  text-align: center;
  flex: 1;
}

.about-stat-num {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-accent);
  font-family: var(--font-serif);
}

.about-stat-label {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  margin-top: 2px;
}

.about-credit {
  font-size: 0.8rem;
  color: var(--color-text-muted);
  text-align: center;
  margin-top: 6px;
}

/* ============================================
   Toast
   ============================================ */
.toast {
  position: fixed;
  bottom: calc(var(--safe-bottom) + 80px);
  left: 50%;
  transform: translateX(-50%) translateY(20px);
  background: var(--color-text);
  color: var(--color-bg);
  padding: 10px 22px;
  border-radius: 100px;
  font-size: 0.85rem;
  font-weight: 500;
  opacity: 0;
  pointer-events: none;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  z-index: 300;
  white-space: nowrap;
}

.toast.active {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* ============================================
   Mode Toggle Bar
   ============================================ */
.mode-bar {
  display: flex;
  justify-content: center;
  padding: 6px 20px 0;
  max-width: 720px;
  margin: 0 auto;
}

.mode-toggle {
  display: flex;
  background: var(--color-chip-bg);
  border-radius: 100px;
  padding: 4px;
  gap: 2px;
}

.mode-btn {
  padding: 10px 22px;
  border: none;
  background: transparent;
  color: var(--color-text-soft);
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 500;
  border-radius: 100px;
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
}

.mode-btn--active {
  background: var(--color-surface);
  color: var(--color-text);
  box-shadow: var(--shadow-sm);
}

.mode-btn:active {
  transform: scale(0.95);
}

/* --- Header Actions --- */
.header-actions {
  display: flex;
  align-items: center;
  gap: 4px;
}

/* --- Book Badge --- */
.book-badge {
  position: absolute;
  top: 1px;
  right: 1px;
  width: 18px;
  height: 18px;
  background: var(--color-accent-alt);
  color: #fff;
  font-size: 0.65rem;
  font-weight: 700;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  line-height: 1;
}

.btn-icon {
  position: relative;
}

/* ============================================
   Word Book Panel (slide-out from right)
   ============================================ */
.book-overlay {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 250;
  background: rgba(44,62,80,0.3);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
}

.book-overlay.active {
  display: flex;
  justify-content: flex-end;
}

.book-panel {
  width: 100%;
  max-width: 420px;
  height: 100%;
  height: 100dvh;
  background: var(--color-surface);
  display: flex;
  flex-direction: column;
  animation: slideInRight 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  box-shadow: var(--shadow-lg);
}

@keyframes slideInRight {
  from { transform: translateX(100%); }
  to { transform: translateX(0); }
}

.book-header {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 16px 20px;
  border-bottom: 1px solid var(--color-border);
  flex-shrink: 0;
}

.book-title {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 1.1rem;
  font-weight: 650;
  color: var(--color-text);
  flex: 1;
}

.book-count {
  font-size: 0.8rem;
  color: var(--color-text-muted);
  font-weight: 500;
}

.btn-book-close {
  flex-shrink: 0;
}

.book-actions {
  display: flex;
  gap: 8px;
  padding: 12px 20px;
  border-bottom: 1px solid var(--color-border);
  flex-shrink: 0;
}

.chip--danger {
  color: var(--color-danger);
}

.chip--danger:hover {
  background: #F8E8E6;
}

.book-list {
  flex: 1;
  overflow-y: auto;
  padding: 12px 20px;
  -webkit-overflow-scrolling: touch;
}

.book-empty {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 48px 20px;
  text-align: center;
}

.book-empty p {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  margin-top: 12px;
}

/* --- Book Item --- */
.book-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 14px;
  background: var(--color-bg);
  border-radius: var(--radius-md);
  margin-bottom: 8px;
  transition: all var(--transition);
}

.book-item:hover {
  background: var(--color-highlight);
}

.book-item-info {
  flex: 1;
  min-width: 0;
}

.book-item-word {
  font-weight: 650;
  font-size: 0.95rem;
  color: var(--color-text);
}

.book-item-meaning {
  font-size: 0.8rem;
  color: var(--color-text-soft);
  margin-top: 2px;
}

.book-item-meta {
  font-size: 0.72rem;
  color: var(--color-text-muted);
  margin-top: 2px;
}

.book-item-remove {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border: none;
  background: transparent;
  color: var(--color-text-muted);
  border-radius: 50%;
  cursor: pointer;
  flex-shrink: 0;
  transition: all var(--transition);
}

.book-item-remove:hover {
  background: #F8E8E6;
  color: var(--color-danger);
}

/* --- Bookmark Star --- */
.btn-bookmark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border: none;
  background: transparent;
  color: var(--color-text-muted);
  border-radius: 50%;
  cursor: pointer;
  flex-shrink: 0;
  transition: all var(--transition);
  margin-left: auto;
}

.btn-bookmark:hover {
  background: var(--color-highlight);
  color: var(--color-accent-alt);
}

.btn-bookmark--saved {
  color: var(--color-accent-alt);
}

.btn-bookmark--saved svg {
  fill: var(--color-accent-alt);
}

/* ============================================
   Star Button (标星加入生词本)
   ============================================ */
.btn-star-word {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 6px 14px;
  border: 1.5px solid var(--color-border);
  background: transparent;
  color: var(--color-text-muted);
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 500;
  border-radius: 100px;
  cursor: pointer;
  transition: all var(--transition);
  width: auto;
  height: auto;
  white-space: nowrap;
}

.btn-star-word:hover {
  border-color: var(--color-accent-alt);
  color: var(--color-accent-alt);
  background: var(--color-highlight);
}

.btn-star-word:active {
  transform: scale(0.95);
}

.btn-star-word.starred {
  border-color: var(--color-accent-alt);
  color: var(--color-accent-alt);
  background: #FFF5EC;
}

.btn-star-word.starred:hover {
  background: #FFE8D5;
  color: #C0743B;
  border-color: #C0743B;
}

/* ============================================
   Add-to-book Dropdown
   ============================================ */
.add-book-dropdown {
  position: absolute;
  right: 0;
  top: 100%;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-md);
  z-index: 50;
  min-width: 160px;
  max-height: 200px;
  overflow-y: auto;
  animation: fadeIn 0.15s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(-4px); }
  to { opacity: 1; transform: translateY(0); }
}

.add-book-item {
  display: block;
  width: 100%;
  padding: 10px 14px;
  border: none;
  background: transparent;
  text-align: left;
  font-family: var(--font-sans);
  font-size: 0.85rem;
  color: var(--color-text);
  cursor: pointer;
  transition: background var(--transition);
  border-bottom: 1px solid var(--color-border);
}

.add-book-item:last-child {
  border-bottom: none;
}

.add-book-item:hover {
  background: var(--color-highlight);
}

.add-book-item-name {
  font-weight: 500;
}

.add-book-item-count {
  font-size: 0.72rem;
  color: var(--color-text-muted);
  margin-left: 6px;
}

.add-book-item--new {
  color: var(--color-accent) !important;
  font-weight: 600;
  border-top: 1px solid var(--color-border);
}

.add-book-item--new:hover {
  background: #E8F5EF !important;
}

.add-book-item.already-in {
  color: var(--color-accent-alt);
  font-weight: 500;
}

/* ============================================
   Word Book Create Input
   ============================================ */
.book-create {
  display: flex;
  gap: 8px;
  padding: 12px 20px;
  border-bottom: 1px solid var(--color-border);
  flex-shrink: 0;
}

.book-create-input {
  flex: 1;
  padding: 10px 14px;
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-sm);
  font-family: var(--font-sans);
  font-size: 0.9rem;
  color: var(--color-text);
  background: var(--color-bg);
  outline: none;
  transition: border-color var(--transition);
}

.book-create-input:focus {
  border-color: var(--color-accent);
}

.book-create-input::placeholder {
  color: var(--color-text-muted);
}

.btn-create {
  padding: 10px 16px;
  border: none;
  background: var(--color-accent);
  color: #fff;
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 600;
  border-radius: var(--radius-sm);
  cursor: pointer;
  white-space: nowrap;
  transition: all var(--transition);
}

.btn-create:hover {
  opacity: 0.9;
}

.btn-create:active {
  transform: scale(0.95);
}

/* ============================================
   Word Book Card (in book list)
   ============================================ */
.book-card {
  background: var(--color-bg);
  border-radius: var(--radius-md);
  padding: 16px;
  margin-bottom: 10px;
  transition: all var(--transition);
}

.book-card:hover {
  background: var(--color-highlight);
}

.book-card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  margin-bottom: 8px;
}

.book-card-name {
  font-weight: 650;
  font-size: 0.95rem;
  color: var(--color-text);
  flex: 1;
  min-width: 0;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.book-card-actions {
  display: flex;
  gap: 4px;
  flex-shrink: 0;
}

.book-card-action {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 30px;
  height: 30px;
  border: none;
  background: transparent;
  color: var(--color-text-muted);
  border-radius: 50%;
  cursor: pointer;
  transition: all var(--transition);
}

.book-card-action:hover {
  background: var(--color-border);
  color: var(--color-text);
}

.book-card-action--study {
  color: var(--color-accent);
}

.book-card-action--delete:hover {
  background: #F8E8E6;
  color: var(--color-danger);
}

.book-card-meta {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 0.78rem;
  color: var(--color-text-soft);
}

.book-card-progress {
  flex: 1;
  height: 5px;
  background: var(--color-border);
  border-radius: 5px;
  overflow: hidden;
}

.book-card-progress-fill {
  height: 100%;
  background: var(--color-accent);
  border-radius: 5px;
  transition: width 0.3s ease;
}

/* ============================================
   Study Mode (Fullscreen Flashcard)
   ============================================ */
.study-overlay {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 300;
  background: var(--color-bg);
  flex-direction: column;
}

.study-overlay.active {
  display: flex;
}

.study-container {
  display: flex;
  flex-direction: column;
  height: 100%;
  height: 100dvh;
  max-width: 560px;
  margin: 0 auto;
  width: 100%;
  padding: 0 20px;
}

/* --- Top Bar --- */
.study-topbar {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 0;
  flex-shrink: 0;
}

.study-info {
  flex: 1;
  display: flex;
  flex-direction: column;
  min-width: 0;
}

.study-book-name {
  font-size: 0.95rem;
  font-weight: 650;
  color: var(--color-text);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.study-counter {
  font-size: 0.78rem;
  color: var(--color-text-soft);
}

/* --- Progress Bar --- */
.study-progress-bar {
  height: 4px;
  background: var(--color-border);
  border-radius: 4px;
  overflow: hidden;
  flex-shrink: 0;
  margin-bottom: 8px;
}

.study-progress-fill {
  height: 100%;
  background: var(--color-accent);
  border-radius: 4px;
  transition: width 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

/* --- Flashcard --- */
.study-card-area {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  perspective: 1000px;
  padding: 16px 0;
}

.flashcard {
  width: 100%;
  max-width: 360px;
  aspect-ratio: 3 / 4;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}

.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1);
  transform-style: preserve-3d;
}

.flashcard-inner.flipped {
  transform: rotateY(180deg);
}

.flashcard-front,
.flashcard-back {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 16px;
  padding: 32px 24px;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-lg);
}

.flashcard-front {
  background: var(--color-surface);
  border: 2px solid var(--color-border);
}

.flashcard-back {
  background: var(--color-surface);
  border: 2px solid var(--color-accent);
  transform: rotateY(180deg);
}

.flashcard-word {
  font-family: var(--font-serif);
  font-size: 2rem;
  font-weight: 700;
  color: var(--color-text);
  text-align: center;
  letter-spacing: 0.02em;
}

.flashcard-hint {
  font-size: 0.82rem;
  color: var(--color-text-muted);
}

.flashcard-meaning {
  font-size: 1.3rem;
  font-weight: 650;
  color: var(--color-accent);
  text-align: center;
}

.flashcard-example {
  font-size: 0.9rem;
  color: var(--color-text-soft);
  text-align: center;
  font-style: italic;
  line-height: 1.5;
  padding: 12px 16px;
  background: var(--color-bg);
  border-radius: var(--radius-sm);
  width: 100%;
}

.flashcard-collocations {
  font-size: 0.78rem;
  color: var(--color-accent);
  text-align: center;
  line-height: 1.4;
  padding: 4px 8px;
  width: 100%;
}

.flashcard-source {
  font-size: 0.75rem;
  color: var(--color-text-muted);
}

/* --- Study Actions --- */
.study-actions {
  display: flex;
  gap: 16px;
  padding: 20px 0;
  padding-bottom: calc(var(--safe-bottom) + 20px);
  flex-shrink: 0;
}

.study-btn {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 16px;
  border: none;
  border-radius: var(--radius-lg);
  font-family: var(--font-sans);
  font-size: 1rem;
  font-weight: 650;
  cursor: pointer;
  transition: all var(--transition);
}

.study-btn--forgot {
  background: #F8E8E6;
  color: var(--color-danger);
}

.study-btn--forgot:hover {
  background: #F0D8D5;
}

.study-btn--known {
  background: #E1EFE6;
  color: #4A8A6A;
}

.study-btn--known:hover {
  background: #D0E8D6;
}

.study-btn:active {
  transform: scale(0.95);
}

/* --- Study Complete --- */
.study-complete {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 12px;
  text-align: center;
}

.study-complete-icon {
  font-size: 3rem;
  margin-bottom: 8px;
}

.study-complete h3 {
  font-size: 1.2rem;
  color: var(--color-text);
}

.study-complete p {
  font-size: 0.9rem;
  color: var(--color-text-soft);
  margin-bottom: 8px;
}

.study-complete-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: center;
}

.study-complete-actions .chip {
  font-size: 0.85rem;
  padding: 10px 18px;
}

/* ============================================
   Word Search Cards
   ============================================ */
.word-search-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: 20px;
  margin-bottom: 14px;
  box-shadow: var(--shadow-sm);
  border: 1px solid transparent;
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}

.word-search-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
  border-color: var(--color-border);
}

.word-search-card::after {
  content: '';
  position: absolute;
  top: 0; left: 0;
  width: 4px; height: 100%;
  background: var(--card-accent, var(--color-accent));
  opacity: 0;
  transition: opacity var(--transition);
}

.word-search-card:hover::after { opacity: 1; }

.word-search-header {
  display: flex;
  flex-direction: column;
  gap: 4px;
  margin-bottom: 10px;
}

.word-search-title {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.word-search-word {
  font-family: var(--font-serif);
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--color-text);
  letter-spacing: -0.01em;
}

.word-search-meaning {
  font-size: 0.95rem;
  color: var(--color-text-soft);
  font-weight: 500;
}

.word-search-sources {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-bottom: 12px;
}

.word-src-tag {
  display: inline-flex;
  align-items: center;
  padding: 2px 10px;
  border-radius: 100px;
  font-size: 0.7rem;
  font-weight: 500;
  color: var(--color-text-muted);
  background: var(--color-chip-bg);
}

.word-search-section-label {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 8px;
}

.word-search-collocations {
  margin-bottom: 10px;
}

.collocation-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.collocation-chip {
  display: inline-flex;
  align-items: center;
  padding: 5px 12px;
  border-radius: 8px;
  background: var(--color-highlight);
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--color-accent);
  transition: all var(--transition);
}

.collocation-chip:hover {
  background: var(--color-border);
  color: var(--color-text);
}

.collocation-chip.empty {
  color: var(--color-text-muted);
  background: var(--color-bg);
  font-style: italic;
}

.word-example-label {
  display: inline-block;
  font-size: 0.7rem;
  font-weight: 600;
  color: var(--color-accent-alt);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-right: 8px;
  background: var(--color-highlight);
  padding: 2px 8px;
  border-radius: 4px;
}

.word-search-card .word-example {
  font-size: 0.85rem;
  color: var(--color-text-soft);
  font-style: italic;
  padding: 10px 14px;
  background: var(--color-bg);
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--color-accent);
  line-height: 1.6;
}

.word-search-card .word-nuance {
  font-size: 0.82rem;
  color: var(--color-text-soft);
  margin-bottom: 6px;
  padding: 6px 10px;
  background: var(--color-highlight);
  border-radius: var(--radius-sm);
}

.word-search-card .word-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  font-size: 0.75rem;
  color: var(--color-text-muted);
  margin-bottom: 6px;
}

.word-search-card .prefix-tag {
  color: var(--color-accent);
  font-weight: 500;
}

.word-search-card .suffix-tag {
  color: var(--color-accent-blue);
  font-weight: 500;
}

.word-search-card .btn-bookmark {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 6px 14px;
  border: none;
  background: var(--color-chip-bg);
  color: var(--color-text-soft);
  font-family: var(--font-sans);
  font-size: 0.8rem;
  font-weight: 500;
  border-radius: 100px;
  cursor: pointer;
  transition: all var(--transition);
  width: auto;
  height: auto;
}

.word-search-card .btn-bookmark:hover {
  background: var(--color-highlight);
  color: var(--color-accent-alt);
}

/* ============================================
   Responsive
   ============================================ */
@media (max-width: 480px) {
  .header-inner {
    padding: 10px 16px;
    height: 52px;
  }

  :root {
    --header-h: 52px;
    --search-h: 66px;
    --nav-h: 46px;
  }

  .search-section {
    padding: 6px 16px 10px;
  }

  .category-nav {
    padding: 0 16px 6px;
  }

  .main-content {
    padding: 12px 16px 28px;
  }

  .root-card {
    padding: 16px;
  }

  .card-root {
    font-size: 1.2rem;
  }

  .modal {
    border-radius: var(--radius-lg) var(--radius-lg) 0 0;
    margin: 10vh 0 0 0;
    max-height: 85vh;
    overflow-y: auto;
    align-self: flex-end;
  }

  @keyframes modalIn {
    from {
      opacity: 0;
      transform: translateY(40px);
    }
    to {
      opacity: 1;
      transform: translateY(0);
    }
  }

  .mode-bar {
    padding: 4px 16px 0;
  }

  .mode-btn {
    padding: 8px 16px;
    font-size: 0.8rem;
  }

  .book-panel {
    max-width: 100%;
  }

  .mode-btn {
    padding: 6px 12px;
    font-size: 0.78rem;
  }
}

/* ============================================
   Word Phonetic
   ============================================ */
.word-phonetic {
  font-size: 0.78rem;
  color: var(--color-text-muted);
  font-family: var(--font-serif);
  margin-left: 8px;
}

/* ============================================
   Distinction Card
   ============================================ */
.distinction-card {
  background: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: 20px;
  cursor: pointer;
  transition: all var(--transition);
  border: 1px solid transparent;
  box-shadow: var(--shadow-sm);
  position: relative;
  overflow: hidden;
}

.distinction-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
}

.distinction-card:active {
  transform: scale(0.985);
  background: var(--color-highlight);
}

.distinction-card::after {
  content: '';
  position: absolute;
  top: 0; left: 0;
  width: 4px; height: 100%;
  background: var(--color-accent);
  opacity: 0;
  transition: opacity var(--transition);
}

.distinction-card:hover::after { opacity: 1; }

.distinction-card .card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 8px;
}

.distinction-title {
  font-family: var(--font-serif);
  font-size: 1.2rem;
  font-weight: 700;
  color: var(--color-text);
  letter-spacing: -0.01em;
}

.distinction-chinese {
  font-size: 0.9rem;
  color: var(--color-text-soft);
}

.distinction-preview {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 10px;
}

.distinction-word-chip {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 5px 12px;
  background: var(--color-bg);
  border-radius: 8px;
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--color-text);
}

.distinction-word-chip .dw-arrow {
  color: var(--color-text-muted);
  font-size: 0.7rem;
}

/* ============================================
   Distinction Detail
   ============================================ */
.distinction-detail-word {
  background: var(--color-bg);
  border-radius: var(--radius-md);
  padding: 16px;
  margin-bottom: 12px;
  border-left: 3px solid var(--color-accent);
}

.distinction-detail-word h4 {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1.1rem;
  margin-bottom: 6px;
}

.distinction-detail-word .word-name {
  font-family: var(--font-serif);
  color: var(--color-text);
}

.distinction-detail-word .word-phonetic-detail {
  font-size: 0.82rem;
  color: var(--color-text-muted);
  font-family: var(--font-serif);
  font-weight: 400;
}

.distinction-detail-word .word-nuance {
  font-size: 0.85rem;
  color: var(--color-text-soft);
  margin-bottom: 6px;
  padding: 6px 10px;
  background: var(--color-highlight);
  border-radius: var(--radius-sm);
}

.distinction-detail-word .word-example {
  font-size: 0.83rem;
  color: var(--color-text-soft);
  font-style: italic;
  margin-bottom: 4px;
}

.distinction-detail-word .word-collocations {
  font-size: 0.78rem;
  color: var(--color-text-muted);
}

/* ============================================
   Pre-built Book Card
   ============================================ */
.prebuilt-section {
  padding: 0 20px 12px;
  border-bottom: 1px solid var(--color-border);
  flex-shrink: 0;
}

.prebuilt-title {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 8px;
}

.prebuilt-card {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 14px;
  background: var(--color-bg);
  border-radius: var(--radius-sm);
  margin-bottom: 6px;
  transition: all var(--transition);
}

.prebuilt-card:hover {
  background: var(--color-highlight);
}

.prebuilt-card-info {
  flex: 1;
  min-width: 0;
}

.prebuilt-card-name {
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--color-text);
}

.prebuilt-card-desc {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  margin-top: 2px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.prebuilt-card-import {
  padding: 6px 14px;
  border: none;
  background: var(--color-accent);
  color: #fff;
  font-family: var(--font-sans);
  font-size: 0.78rem;
  font-weight: 600;
  border-radius: 100px;
  cursor: pointer;
  white-space: nowrap;
  transition: all var(--transition);
  flex-shrink: 0;
}

.prebuilt-card-import:hover { opacity: 0.9; }
.prebuilt-card-import:active { transform: scale(0.92); }
.prebuilt-card-import.imported { background: var(--color-text-muted); pointer-events: none; }