:root {
    --primary-color: #2c3e50;
    --accent-color: #3498db;
    --accent-hover: #2980b9;
    --bg-color: #f5f7fa;
    --card-bg: #ffffff;
    --text-color: #333333;
    --text-secondary: #64748b;
    --text-light: #94a3b8;
    --border-color: #e2e8f0;
    --correct-color: #27ae60;
    --incorrect-color: #e74c3c;
    --warning-color: #f39c12;
    --sidebar-width: 320px;
    --header-height: 64px;
    --bottom-bar-height: 70px;
    --card-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.08), 0 8px 10px -6px rgba(0, 0, 0, 0.04);
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    -webkit-tap-highlight-color: transparent;
}

body, html {
    height: 100%;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, "Noto Sans TC", sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    overflow-x: hidden;
    -webkit-overflow-scrolling: touch;
}

.layout-container {
    display: flex;
    height: 100vh;
    height: 100dvh;
    overflow: hidden;
    position: relative;
}

/* ==================== 側邊欄 / 抽屜 ==================== */
.sidebar {
    width: var(--sidebar-width);
    background-color: #ffffff;
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    height: 100%;
    overflow-y: auto;
    z-index: 100;
    transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.sidebar-header {
    padding: 18px 20px 14px;
    border-bottom: 1px solid var(--border-color);
    background: #ffffff;
    position: sticky;
    top: 0;
    z-index: 10;
}

.sidebar-title-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.sidebar-title-row h2 {
    font-size: 1.35rem;
    color: var(--primary-color);
    font-weight: 700;
    letter-spacing: -0.02em;
}

.mobile-close-sidebar-btn {
    display: none;
    background: none;
    border: none;
    font-size: 1.4rem;
    color: var(--text-secondary);
    cursor: pointer;
    padding: 4px;
}

.sidebar-subtitle {
    font-size: 0.8rem;
    color: var(--text-secondary);
    margin-top: 2px;
    margin-bottom: 12px;
}

.season-selector-wrapper {
    margin-bottom: 12px;
}

.filter-label {
    display: block;
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: 4px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.theme-select {
    width: 100%;
    padding: 8px 12px;
    font-size: 0.88rem;
    font-weight: 600;
    color: var(--primary-color);
    background-color: #f8fafc;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    outline: none;
    cursor: pointer;
    transition: all 0.2s;
}

.theme-select:focus {
    border-color: var(--accent-color);
    box-shadow: 0 0 0 2px rgba(52, 152, 219, 0.2);
}

/* 標籤按鈕 */
.category-tabs {
    display: flex;
    gap: 6px;
}

.cat-tab {
    flex: 1;
    padding: 7px 4px;
    font-size: 0.82rem;
    font-weight: 600;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    background: #f8fafc;
    color: var(--text-secondary);
    cursor: pointer;
    transition: all 0.2s;
    text-align: center;
}

.cat-tab:hover {
    background: #f1f5f9;
    color: var(--text-color);
}

.cat-tab.active {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

/* 側邊欄清單 */
.sidebar-menu {
    padding: 12px 0 30px;
    flex: 1;
}

.menu-category {
    padding: 10px 20px 6px;
    font-size: 0.78rem;
    color: #7f8c8d;
    text-transform: uppercase;
    letter-spacing: 1px;
    font-weight: 700;
}

.menu-list {
    list-style: none;
}

.menu-list li {
    padding: 11px 20px;
    cursor: pointer;
    border-left: 3px solid transparent;
    transition: all 0.15s;
    font-size: 0.9rem;
    color: #475569;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.menu-list li:hover {
    background-color: #f8fafc;
    border-left-color: #cbd5e1;
    color: var(--text-color);
}

.menu-list li.active {
    background-color: #ebf5fb;
    border-left-color: var(--accent-color);
    font-weight: 700;
    color: var(--accent-color);
}

.menu-count-pill {
    font-size: 0.75rem;
    padding: 2px 7px;
    border-radius: 10px;
    background: #e2e8f0;
    color: #64748b;
    font-weight: 600;
}

.menu-list li.active .menu-count-pill {
    background: #dbeafe;
    color: var(--accent-color);
}

.sidebar-overlay {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(15, 23, 42, 0.4);
    backdrop-filter: blur(2px);
    z-index: 90;
}

/* ==================== 主內容區域 ==================== */
.main-area {
    flex: 1;
    display: flex;
    flex-direction: column;
    height: 100%;
    overflow-y: auto;
    -webkit-overflow-scrolling: touch;
    touch-action: pan-y;
    position: relative;
    background-color: var(--bg-color);
}

/* 頂部應用導覽列 */
.app-header {
    height: var(--header-height);
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 24px;
    background: #ffffff;
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 30;
}

.header-left {
    display: flex;
    align-items: center;
    gap: 12px;
}

.mobile-menu-btn {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    color: var(--primary-color);
    padding: 6px;
    border-radius: 6px;
}

.mobile-menu-btn:hover {
    background-color: #f1f5f9;
}

.title-group {
    display: flex;
    align-items: center;
    gap: 10px;
}

.title-group h1 {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary-color);
}

.active-season-badge {
    font-size: 0.75rem;
    font-weight: 600;
    padding: 3px 10px;
    background: #ebf5fb;
    color: var(--accent-color);
    border-radius: 12px;
    border: 1px solid rgba(52, 152, 219, 0.2);
}

.header-right {
    display: flex;
    align-items: center;
    gap: 10px;
}

/* 模式切換按鈕 */
.view-mode-toggle {
    display: flex;
    background: #f1f5f9;
    padding: 3px;
    border-radius: 8px;
    border: 1px solid var(--border-color);
}

.toggle-mode-btn {
    border: none;
    background: none;
    padding: 5px 12px;
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-secondary);
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.15s;
}

.toggle-mode-btn.active {
    background: #ffffff;
    color: var(--primary-color);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
}

/* 按鈕樣式規範 (延續 IELTS 原專案) */
button,
.btn,
.cat-tab,
.topic-chip,
.toggle-mode-btn,
.speed-btn,
.nav-card-btn,
.flip-card-btn,
.random-btn,
.play-audio-btn,
.gemini-btn,
.back-flip-return-btn,
.status-action-btn,
.clear-search-btn,
.modal-actions .btn {
    white-space: nowrap !important;
    word-break: keep-all !important;
    flex-shrink: 0;
}

.btn {
    padding: 8px 16px;
    border-radius: 6px;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 6px;
    transition: all 0.2s;
    border: none;
    white-space: nowrap !important;
}

.primary-btn {
    background-color: var(--accent-color);
    color: white;
}
.primary-btn:hover {
    background-color: var(--accent-hover);
}

.outline-btn {
    background-color: transparent;
    border: 1px solid var(--border-color);
    color: var(--primary-color);
}
.outline-btn:hover {
    background-color: #f8fafc;
    border-color: #cbd5e1;
}

.secondary-btn {
    background-color: #64748b;
    color: white;
}
.secondary-btn:hover {
    background-color: #475569;
}

.danger-btn {
    color: var(--incorrect-color);
    border-color: rgba(231, 76, 60, 0.3);
}
.danger-btn:hover {
    background-color: var(--incorrect-bg);
}

/* 頂部快速篩選列 */
.top-filter-bar {
    background: #ffffff;
    border-bottom: 1px solid var(--border-color);
    padding: 10px 24px;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.search-box-wrapper {
    position: relative;
    display: flex;
    align-items: center;
}

.search-icon {
    position: absolute;
    left: 12px;
    font-size: 0.85rem;
    color: var(--text-light);
    pointer-events: none;
}

.search-input {
    width: 100%;
    padding: 9px 36px 9px 36px;
    font-size: 0.9rem;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    background: #f8fafc;
    outline: none;
    transition: all 0.2s;
}

.search-input:focus {
    background: #ffffff;
    border-color: var(--accent-color);
    box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.15);
}

.clear-search-btn {
    position: absolute;
    right: 10px;
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 0.9rem;
    cursor: pointer;
    padding: 4px;
}

/* 話題滾動標籤 */
.horizontal-topic-scroll {
    display: flex;
    gap: 8px;
    overflow-x: auto;
    padding-bottom: 4px;
    scrollbar-width: none;
    -ms-overflow-style: none;
}
.horizontal-topic-scroll::-webkit-scrollbar {
    display: none;
}

.topic-chip {
    flex-shrink: 0;
    padding: 5px 12px;
    font-size: 0.8rem;
    font-weight: 600;
    border-radius: 20px;
    background: #f1f5f9;
    color: var(--text-secondary);
    border: 1px solid transparent;
    cursor: pointer;
    transition: all 0.15s;
}

.topic-chip:hover {
    background: #e2e8f0;
    color: var(--text-color);
}

.topic-chip.active {
    background: var(--accent-color);
    color: white;
}

/* ==================== 主工作容器 ==================== */
.content-container {
    flex: 1;
    padding: 20px 24px calc(var(--bottom-bar-height) + 20px);
    display: flex;
    flex-direction: column;
    max-width: 900px;
    margin: 0 auto;
    width: 100%;
}

.view-panel {
    display: none;
    width: 100%;
}
.view-panel.active {
    display: block;
}

/* 卡片狀態列 */
.card-status-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
    padding: 0 4px;
}

.status-left {
    display: flex;
    align-items: center;
    gap: 8px;
    flex-wrap: nowrap;
    overflow-x: auto;
    scrollbar-width: none;
}
.status-left::-webkit-scrollbar {
    display: none;
}

.card-counter, .card-category-badge, .card-part-badge {
    white-space: nowrap !important;
    flex-shrink: 0;
}

.card-counter {
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--primary-color);
}

.card-category-badge {
    font-size: 0.75rem;
    font-weight: 600;
    padding: 2px 8px;
    border-radius: 4px;
    background: #e2e8f0;
    color: #475569;
}

.card-part-badge {
    font-size: 0.75rem;
    font-weight: 700;
    padding: 2px 8px;
    border-radius: 4px;
    background: #fef3c7;
    color: #92400e;
    border: 1px solid #fde68a;
}

.status-right {
    display: flex;
    gap: 8px;
    flex-shrink: 0;
}

.status-action-btn {
    background: #ffffff;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    color: var(--text-secondary);
    transition: all 0.15s;
    padding: 0;
}

.status-action-btn:hover {
    background: #f8fafc;
}

.status-action-btn.starred {
    border-color: #fcd34d;
    background: #fffbeb;
}

.status-action-btn.starred .star-icon-svg {
    fill: #f59e0b;
    stroke: #f59e0b;
}

.status-action-btn.mastered {
    border-color: #86efac;
    background: #f0fdf4;
}

.status-action-btn.mastered .check-icon-svg {
    stroke: var(--correct-color);
}

/* ==================== SVG 圖示統一樣式 ==================== */
.btn-svg,
.nav-icon-svg,
.flip-icon-svg,
.random-icon-svg,
.search-icon-svg,
.audio-icon-svg,
.star-icon-svg,
.check-icon-svg {
    display: inline-block;
    vertical-align: middle;
    flex-shrink: 0;
}

/* ==================== 3D 翻轉卡片系統 ==================== */
.flashcard-scene {
    perspective: 1200px;
    width: 100%;
    min-height: 480px;
    margin-bottom: 20px;
    transition: height 0.25s ease-out;
}

.flashcard {
    width: 100%;
    min-height: 480px;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.55s cubic-bezier(0.2, 0.8, 0.2, 1), height 0.25s ease-out;
    border-radius: 16px;
    box-shadow: var(--card-shadow);
}

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

.flashcard-face {
    position: absolute;
    width: 100%;
    height: 100%;
    min-height: 480px;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    border-radius: 16px;
    background-color: var(--card-bg);
    border: 1px solid var(--border-color);
    padding: 26px 28px;
    display: flex;
    flex-direction: column;
    overflow-y: auto;
    -webkit-overflow-scrolling: touch;
    touch-action: pan-y;
}

/* 正面 */
.flashcard-front {
    cursor: pointer;
}

.card-face-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-bottom: 14px;
    border-bottom: 1px solid #f1f5f9;
    margin-bottom: 18px;
}

.card-topic-title {
    font-size: 0.95rem;
    font-weight: 700;
    color: var(--accent-color);
}

.card-season-tag {
    font-size: 0.75rem;
    color: var(--text-light);
    font-weight: 500;
}

.question-main-area {
    margin-bottom: 20px;
}

.q-label {
    font-size: 0.72rem;
    font-weight: 800;
    color: var(--text-light);
    letter-spacing: 1.5px;
    margin-bottom: 6px;
}

.question-text {
    font-size: 1.35rem;
    font-weight: 700;
    color: #1e293b;
    line-height: 1.45;
    margin-bottom: 16px;
}

/* Part 2 Cue bullets */
.cue-card-bullets {
    background: #f8fafc;
    border-left: 3px solid var(--accent-color);
    padding: 14px 18px;
    border-radius: 0 8px 8px 0;
    margin-bottom: 18px;
}

.cue-label {
    font-size: 0.85rem;
    font-weight: 700;
    color: #334155;
    margin-bottom: 8px;
}

.cue-bullets-list {
    list-style-type: disc;
    padding-left: 20px;
    color: #475569;
    font-size: 0.92rem;
    line-height: 1.6;
}

/* 語音按鈕 */
.audio-control-bar {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-top: 8px;
    flex-wrap: wrap;
}

.play-audio-btn {
    background-color: #f1f5f9;
    color: var(--primary-color);
    border: 1px solid #cbd5e1;
    padding: 7px 14px;
    font-size: 0.86rem;
    border-radius: 8px;
}
.play-audio-btn:hover {
    background-color: #e2e8f0;
}
.play-audio-btn.is-speaking {
    background-color: #e0f2fe;
    border-color: var(--accent-color);
    color: var(--accent-color);
    animation: pulse-border 1.5s infinite;
}

@keyframes pulse-border {
    0% { box-shadow: 0 0 0 0 rgba(52, 152, 219, 0.4); }
    70% { box-shadow: 0 0 0 6px rgba(52, 152, 219, 0); }
    100% { box-shadow: 0 0 0 0 rgba(52, 152, 219, 0); }
}

.voice-badge {
    font-size: 0.75rem;
    color: var(--text-light);
    font-weight: 500;
}

/* 提示區塊 */
.tips-container {
    background: #fffdf5;
    border: 1px solid #fef3c7;
    border-radius: 10px;
    margin-top: auto;
    margin-bottom: 14px;
    overflow: visible;
}

.tips-header {
    padding: 10px 14px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: #fef9c3;
    cursor: pointer;
    user-select: none;
}

.tips-header-title {
    font-size: 0.85rem;
    font-weight: 700;
    color: #854d0e;
}

.tips-expand-indicator {
    font-size: 0.75rem;
    color: #854d0e;
    transition: transform 0.2s;
}

.tips-content {
    padding: 14px;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.tip-block {
    font-size: 0.85rem;
    line-height: 1.5;
}

.tip-label {
    font-weight: 700;
    color: #713f12;
    display: inline-block;
    margin-bottom: 2px;
}

.tip-text {
    color: #475569;
}

.collocations-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    margin-top: 4px;
}

.colloc-tag {
    font-size: 0.78rem;
    font-weight: 600;
    background: #ffffff;
    border: 1px solid #fde047;
    color: #854d0e;
    padding: 2px 8px;
    border-radius: 4px;
}

.card-face-footer {
    text-align: center;
    padding-top: 10px;
}

.flip-hint-text {
    font-size: 0.8rem;
    color: var(--text-light);
    font-weight: 600;
}

/* 背面 */
.flashcard-back {
    transform: rotateY(180deg);
    background-color: #ffffff;
}

.back-header {
    border-bottom: 2px solid #f1f5f9;
}

.back-title-badge {
    font-size: 0.75rem;
    font-weight: 800;
    letter-spacing: 1px;
    color: var(--accent-color);
}

.back-part-badge {
    font-size: 0.75rem;
    font-weight: 700;
    background: #e0f2fe;
    color: #0369a1;
    padding: 2px 8px;
    border-radius: 4px;
    margin-left: 8px;
}

.back-flip-return-btn {
    border: none;
    background: #f1f5f9;
    padding: 4px 10px;
    font-size: 0.8rem;
    font-weight: 600;
    border-radius: 6px;
    cursor: pointer;
    color: var(--primary-color);
}
.back-flip-return-btn:hover {
    background: #e2e8f0;
}

.answer-scroll-area {
    flex: 1;
    overflow-y: auto;
    padding-right: 4px;
    display: flex;
    flex-direction: column;
    gap: 14px;
}

/* Part 3 觀點、原因、例子結構 */
.structured-answer-block {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.pre-item {
    background: #f8fafc;
    border-radius: 8px;
    padding: 12px 14px;
    border-left: 4px solid #cbd5e1;
}

.pre-point {
    border-left-color: #3b82f6;
    background: #eff6ff;
}

.pre-reason {
    border-left-color: #8b5cf6;
    background: #f5f3ff;
}

.pre-example {
    border-left-color: #10b981;
    background: #ecfdf5;
}

.pre-conclusion {
    border-left-color: #f59e0b;
    background: #fffbeb;
}

.pre-badge {
    font-size: 0.8rem;
    font-weight: 800;
    color: #1e293b;
    margin-bottom: 4px;
}

.pre-content {
    font-size: 0.95rem;
    line-height: 1.6;
    color: #334155;
}

/* Part 2 Monologue */
.p2-structure-guide {
    font-size: 0.85rem;
    color: var(--text-secondary);
    background: #f1f5f9;
    padding: 10px 14px;
    border-radius: 6px;
    margin-bottom: 6px;
}

.monologue-box, .p1-answer-box {
    background: #f8fafc;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 16px;
}

.monologue-title, .p1-title {
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 8px;
}

.monologue-text, .p1-text {
    font-size: 0.95rem;
    line-height: 1.7;
    color: #1e293b;
}

/* 背面操作欄 */
.back-action-bar {
    display: flex;
    gap: 10px;
    margin-top: 10px;
    flex-wrap: wrap;
}

.gemini-btn {
    background: linear-gradient(135deg, #4f46e5 0%, #7c3aed 100%);
    color: white;
}
.gemini-btn:hover {
    opacity: 0.95;
}

/* Gemini 結果區 */
.gemini-result-container {
    background: #faf5ff;
    border: 1px solid #e9d5ff;
    border-radius: 8px;
    padding: 14px;
    margin-top: 10px;
}

.gemini-result-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.85rem;
    font-weight: 700;
    color: #6b21a8;
    margin-bottom: 8px;
}

.close-gemini-btn {
    background: none;
    border: none;
    cursor: pointer;
    color: #9333ea;
    font-size: 0.9rem;
}

.gemini-result-body {
    font-size: 0.9rem;
    line-height: 1.6;
    color: #3b0764;
    white-space: pre-wrap;
}

/* ==================== 手機底部固定操作列 (按鈕絕不折行) ==================== */
.mobile-bottom-controls {
    position: fixed;
    bottom: 0;
    left: var(--sidebar-width);
    right: 0;
    height: var(--bottom-bar-height);
    background: #ffffff;
    border-top: 1px solid var(--border-color);
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 12px;
    padding: 0 16px;
    box-shadow: 0 -4px 15px rgba(0, 0, 0, 0.05);
    z-index: 40;
    transition: left 0.3s;
}

.nav-card-btn {
    background: #f1f5f9;
    color: var(--primary-color);
    padding: 10px 16px;
    border-radius: 10px;
    font-size: 0.88rem;
    white-space: nowrap !important;
    display: inline-flex;
    align-items: center;
    gap: 6px;
}
.nav-card-btn:hover {
    background: #e2e8f0;
}

.flip-card-btn {
    padding: 10px 22px;
    border-radius: 24px;
    font-size: 0.92rem;
    font-weight: 700;
    white-space: nowrap !important;
    display: inline-flex;
    align-items: center;
    gap: 6px;
    box-shadow: 0 4px 12px rgba(52, 152, 219, 0.3);
}

.random-btn {
    padding: 10px 14px;
    border-radius: 10px;
    font-size: 0.88rem;
    white-space: nowrap !important;
    display: inline-flex;
    align-items: center;
    gap: 6px;
}

/* ==================== 清單檢視模式 ==================== */
.list-summary-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: 14px;
    padding: 0 4px;
}

.list-hint {
    font-size: 0.8rem;
    color: var(--text-light);
}

.questions-list-container {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.list-question-item {
    background: #ffffff;
    border: 1px solid var(--border-color);
    border-radius: 10px;
    padding: 16px 20px;
    cursor: pointer;
    transition: all 0.2s;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.03);
}

.list-question-item:hover {
    border-color: var(--accent-color);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.06);
}

.item-top-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 8px;
}

.item-badges {
    display: flex;
    gap: 6px;
    align-items: center;
}

.item-q-title {
    font-size: 1.05rem;
    font-weight: 600;
    color: #1e293b;
    line-height: 1.45;
}

/* ==================== 設定彈窗 ==================== */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(15, 23, 42, 0.5);
    backdrop-filter: blur(4px);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 200;
    padding: 20px;
}

.modal-content {
    background: #ffffff;
    border-radius: 14px;
    max-width: 500px;
    width: 100%;
    padding: 24px;
    box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    max-height: 90vh;
    overflow-y: auto;
}

.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    padding-bottom: 10px;
    border-bottom: 1px solid var(--border-color);
}

.modal-header h2 {
    font-size: 1.25rem;
    color: var(--primary-color);
}

.modal-close-icon {
    background: none;
    border: none;
    font-size: 1.2rem;
    cursor: pointer;
    color: var(--text-secondary);
}

.settings-group {
    margin-bottom: 20px;
}

.settings-label {
    display: block;
    font-size: 0.9rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 6px;
}

.settings-desc {
    font-size: 0.8rem;
    color: var(--text-secondary);
    margin-bottom: 8px;
}

.radio-options {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.radio-label {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 0.88rem;
    cursor: pointer;
}

.speed-buttons {
    display: flex;
    gap: 8px;
}

.speed-btn {
    flex: 1;
    padding: 8px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    background: #f8fafc;
    font-size: 0.82rem;
    font-weight: 600;
    color: var(--text-secondary);
    cursor: pointer;
    transition: all 0.15s;
}

.speed-btn.active {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
}

.settings-input {
    width: 100%;
    padding: 10px 12px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 0.9rem;
    outline: none;
}
.settings-input:focus {
    border-color: var(--accent-color);
}

.modal-actions {
    display: flex;
    justify-content: flex-end;
    gap: 10px;
    margin-top: 24px;
    padding-top: 14px;
    border-top: 1px solid var(--border-color);
}

/* ==================== 響應式手機端優化 (Mobile-First) ==================== */
@media (max-width: 900px) {
    .sidebar {
        position: fixed;
        top: 0;
        left: 0;
        bottom: 0;
        transform: translateX(-100%);
        box-shadow: 4px 0 20px rgba(0, 0, 0, 0.15);
    }

    .sidebar.open {
        transform: translateX(0);
    }

    .sidebar-overlay.active {
        display: block;
    }

    .mobile-menu-btn {
        display: inline-flex;
    }

    .mobile-close-sidebar-btn {
        display: inline-block;
    }

    .mobile-bottom-controls {
        left: 0;
    }

    .content-container {
        padding: 14px 14px calc(var(--bottom-bar-height) + 14px);
    }

    .flashcard-face {
        padding: 20px 18px;
        min-height: 440px;
    }

    .question-text {
        font-size: 1.15rem;
    }

    .pre-content, .monologue-text, .p1-text {
        font-size: 0.9rem;
    }

    .icon-only-mobile .btn-text {
        display: none;
    }

    .title-group h1 {
        font-size: 1.1rem;
    }

    .active-season-badge {
        display: none;
    }
}

@media (max-width: 600px) {
    .mobile-bottom-controls {
        left: 0;
        gap: 6px;
        padding: 0 6px;
    }

    .nav-card-btn {
        padding: 8px 8px;
        font-size: 0.82rem;
        gap: 4px;
        white-space: nowrap !important;
    }

    .flip-card-btn {
        padding: 8px 12px;
        font-size: 0.85rem;
        gap: 5px;
        white-space: nowrap !important;
    }

    .random-btn {
        padding: 8px 8px;
        font-size: 0.82rem;
        gap: 4px;
        white-space: nowrap !important;
    }

    .top-filter-bar {
        padding: 8px 12px;
    }

    .app-header {
        padding: 0 12px;
    }
}