:root {
    --bg-color: #f4f4f9;
    --surface-color: rgba(255, 255, 255, 0.7);
    --surface-border: rgba(255, 255, 255, 0.5);
    --text-primary: #1e1e24;
    --text-secondary: #5a5a66;
    --accent-color: #6366f1;
    --accent-hover: #4f46e5;
    --success-color: #10b981;
    --sidebar-width: 320px;
    --shadow: 0 4px 30px rgba(0, 0, 0, 0.1);
    --blur: blur(12px);
    --transition-speed: 0.3s;
}

[data-theme="dark"] {
    --bg-color: #0f172a;
    --surface-color: rgba(30, 41, 59, 0.7);
    --surface-border: rgba(255, 255, 255, 0.05);
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --accent-color: #818cf8;
    --accent-hover: #6366f1;
    --success-color: #10b981;
    --shadow: 0 4px 30px rgba(0, 0, 0, 0.3);
}

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

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    transition: background-color var(--transition-speed) ease, color var(--transition-speed) ease;
    overflow: hidden;
}

.app-container {
    display: flex;
    height: 100vh;
    width: 100vw;
}

/* Sidebar */
.sidebar {
    width: var(--sidebar-width);
    background: var(--surface-color);
    backdrop-filter: var(--blur);
    -webkit-backdrop-filter: var(--blur);
    border-right: 1px solid var(--surface-border);
    display: flex;
    flex-direction: column;
    box-shadow: var(--shadow);
    z-index: 10;
    transition: width var(--transition-speed) cubic-bezier(0.4, 0, 0.2, 1), transform var(--transition-speed) cubic-bezier(0.4, 0, 0.2, 1);
    overflow: hidden;
}

.sidebar.collapsed {
    width: 0;
    border-right: none;
    box-shadow: none;
}

.top-actions {
    display: flex;
    gap: 8px;
    margin-left: auto;
}

.search-header {
    padding: 24px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--surface-border);
}

.sidebar-header {
    padding: 24px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--surface-border);
    min-width: var(--sidebar-width);
}

.sidebar-header h1 {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
}

.chapter-list {
    flex: 1;
    overflow-y: auto;
    padding: 16px;
    display: flex;
    flex-direction: column;
    gap: 8px;
    min-width: var(--sidebar-width);
}

.chapter-item {
    background: transparent;
    border: none;
    text-align: left;
    padding: 12px 16px;
    border-radius: 8px;
    font-size: 0.95rem;
    color: var(--text-secondary);
    cursor: pointer;
    transition: all 0.2s ease;
    font-family: inherit;
    line-height: 1.4;
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: relative;
}

.chapter-item:hover {
    background: rgba(128, 128, 128, 0.05);
    color: var(--text-primary);
    transform: translateX(4px);
}

.chapter-item.active {
    background: var(--accent-color);
    color: white;
    font-weight: 500;
    box-shadow: 0 4px 12px rgba(99, 102, 241, 0.3);
}

/* Sidebar item status indicator */
.status-indicator {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background: transparent;
    border: 2px solid var(--text-secondary);
    opacity: 0.5;
    flex-shrink: 0;
    margin-left: 12px;
    transition: all 0.3s ease;
}

.chapter-item.read .status-indicator {
    background: var(--success-color);
    border-color: var(--success-color);
    opacity: 1;
    box-shadow: 0 0 8px rgba(16, 185, 129, 0.5);
}
.chapter-item.active .status-indicator {
    border-color: white;
}
.chapter-item.active.read .status-indicator {
    background: white;
}

/* Main Content */
.main-content {
    flex: 1;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    scroll-behavior: smooth;
    position: relative;
}

.top-bar-container {
    position: sticky;
    top: 0;
    z-index: 20;
    background: var(--bg-color); 
    transition: background-color var(--transition-speed) ease;
}

#progress-container {
    width: 100%;
    height: 4px;
    background: transparent;
}

#reading-progress {
    height: 100%;
    background: var(--accent-color);
    width: 0%;
    transition: width 0.1s ease;
}

.top-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 16px 24px;
    background: var(--surface-color);
    backdrop-filter: var(--blur);
    -webkit-backdrop-filter: var(--blur);
    border-bottom: 1px solid var(--surface-border);
}

.spacer {
    flex-grow: 1;
}

.icon-button {
    background: transparent;
    border: 1px solid transparent;
    color: var(--text-primary);
    cursor: pointer;
    padding: 8px;
    margin-left: 8px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s ease;
}

.icon-button:hover {
    background-color: var(--surface-color);
    border-color: var(--surface-border);
    transform: scale(1.05);
    box-shadow: var(--shadow);
}

.hidden {
    display: none !important;
}

.content-wrapper {
    flex: 1;
    max-width: 800px;
    margin: 0 auto;
    padding: 20px 40px 60px;
    width: 100%;
}

.view {
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.4s ease, transform 0.4s ease;
    display: none;
}

.view.active {
    opacity: 1;
    transform: translateY(0);
    display: block;
}

#welcome-view {
    text-align: center;
    margin-top: 15vh;
}

#welcome-view h2 {
    font-size: 2.5rem;
    margin-bottom: 16px;
    color: var(--text-primary);
}

#welcome-view p {
    font-size: 1.2rem;
    color: var(--text-secondary);
}

/* Search View */
.search-title {
    font-size: 2rem;
    margin-bottom: 24px;
}

.search-input-container {
    margin-bottom: 32px;
}

#search-input {
    width: 100%;
    padding: 16px 24px;
    font-size: 1.2rem;
    border-radius: 12px;
    border: 2px solid var(--surface-border);
    background: var(--surface-color);
    color: var(--text-primary);
    box-shadow: var(--shadow);
    transition: all 0.3s ease;
    font-family: inherit;
    outline: none;
}

#search-input:focus {
    border-color: var(--accent-color);
    box-shadow: 0 4px 20px rgba(99, 102, 241, 0.2);
}

.search-results {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.search-result-item {
    background: var(--surface-color);
    border: 1px solid var(--surface-border);
    padding: 20px;
    border-radius: 12px;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.search-result-item:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow);
    border-color: var(--accent-color);
}

.search-result-title {
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--accent-color);
    margin-bottom: 8px;
}

.search-result-preview {
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.5;
}

.highlight {
    background-color: rgba(250, 204, 21, 0.3);
    color: #eab308;
    font-weight: bold;
    padding: 0 2px;
    border-radius: 2px;
}

/* Reader View */
.chapter-meta {
    font-size: 0.9rem;
    color: var(--text-secondary);
    margin-bottom: 8px;
}

#reader-title {
    font-size: 2.5rem;
    margin-bottom: 32px;
    color: var(--text-primary);
    font-weight: 700;
    line-height: 1.2;
}

#reader-body {
    font-size: 1.15rem;
    color: var(--text-primary);
    line-height: 1.8;
}

#reader-body p {
    margin-bottom: 1.5em;
    text-align: justify;
}

#reader-body .list-item {
    margin-bottom: 0.8em;
    padding-left: 3em;
    text-indent: -1em;
    position: relative;
}

#reader-body .image-container {
    margin: 2em 0;
    text-align: center;
}

#reader-body img {
    max-width: 100%;
    height: auto;
    border-radius: 8px;
    box-shadow: var(--shadow);
}

/* Buttons */
.chapter-actions {
    margin-top: 50px;
    display: flex;
    justify-content: center;
}

.action-btn {
    background: transparent;
    border: 2px solid var(--accent-color);
    color: var(--accent-color);
    padding: 14px 28px;
    border-radius: 30px;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    align-items: center;
    gap: 8px;
}

.action-btn:hover {
    background: rgba(99, 102, 241, 0.1);
    transform: translateY(-2px);
    box-shadow: 0 4px 15px rgba(99, 102, 241, 0.2);
}

.action-btn.active {
    background: var(--success-color);
    border-color: var(--success-color);
    color: white;
}

.action-btn.active:hover {
    background: #059669;
    border-color: #059669;
    box-shadow: 0 4px 15px rgba(16, 185, 129, 0.3);
}

.chapter-navigation {
    margin-top: 50px;
    display: flex;
    justify-content: space-between;
    border-top: 1px solid var(--surface-border);
    padding-top: 30px;
}

.nav-btn {
    background: var(--surface-color);
    border: 1px solid var(--surface-border);
    color: var(--text-primary);
    padding: 14px 24px;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.2s ease;
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 12px;
    box-shadow: var(--shadow);
}

.nav-btn:hover:not(:disabled) {
    background: var(--accent-hover);
    color: white;
    border-color: var(--accent-hover);
    transform: translateY(-2px);
}

.nav-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
    box-shadow: none;
}

/* Scrollbar */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: transparent;
}

::-webkit-scrollbar-thumb {
    background: rgba(128, 128, 128, 0.3);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: rgba(128, 128, 128, 0.5);
}

@media (max-width: 768px) {
    .app-container {
        flex-direction: column;
    }
    .sidebar {
        width: 100%;
        height: 100vh;
        position: fixed;
        z-index: 100;
        left: 0;
        top: 0;
        transition: transform var(--transition-speed) ease;
    }
    .sidebar.collapsed {
        transform: translateX(-100%);
        width: 100%;
        border-right: none;
    }
    .content-wrapper {
        padding: 20px 20px 40px;
    }
    
    .chapter-navigation {
        flex-direction: column;
        gap: 16px;
    }
    .nav-btn {
        width: 100%;
        justify-content: center;
    }
}

/* Quizz View */
.quizz-container {
    max-width: 800px;
    margin: 0 auto;
    padding: 20px;
}

.quizz-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 16px; border-bottom: 1px solid var(--surface-border); padding-bottom: 16px; flex-wrap: wrap; gap: 12px; }

.quizz-overview {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(36px, 1fr));
    gap: 8px;
    margin-bottom: 24px;
    padding: 12px;
    background: var(--surface-color);
    border-radius: 8px;
    border: 1px solid var(--surface-border);
    max-height: 150px;
    overflow-y: auto;
}

.overview-btn {
    width: 100%; aspect-ratio: 1;
    border: 1px solid var(--surface-border);
    border-radius: 4px;
    background: var(--bg-color);
    color: var(--text-secondary);
    font-size: 0.9rem; font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex; align-items: center; justify-content: center;
}

.overview-btn:hover { border-color: var(--accent-color); color: var(--accent-color); }
.overview-btn.active { background: var(--accent-color); color: white; border-color: var(--accent-color); }
.overview-btn.answered-correct { background: var(--success-color); color: white; border-color: var(--success-color); }
.overview-btn.answered-wrong { background: #ef4444; color: white; border-color: #ef4444; }

.quizz-card {
    background: var(--surface-color);
    border: 1px solid var(--surface-border);
    border-radius: 12px;
    padding: 24px;
    box-shadow: var(--shadow);
    margin-bottom: 24px;
}

.quizz-question-text {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 24px;
    color: var(--text-primary);
}

.quizz-options {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.quizz-option {
    padding: 16px;
    background: var(--bg-color);
    border: 2px solid var(--surface-border);
    border-radius: 8px;
    cursor: pointer;
    font-size: 1rem;
    color: var(--text-primary);
    transition: all 0.2s;
    text-align: left;
}

.quizz-option:hover:not(:disabled) {
    border-color: var(--accent-color);
    background: rgba(99, 102, 241, 0.05);
}

.quizz-option.correct {
    background: rgba(34, 197, 94, 0.1);
    border-color: #22c55e;
    color: #166534;
}

[data-theme="dark"] .quizz-option.correct {
    color: #4ade80;
}

.quizz-option.wrong {
    background: rgba(239, 68, 68, 0.1);
    border-color: #ef4444;
    color: #991b1b;
}

[data-theme="dark"] .quizz-option.wrong {
    color: #f87171;
}

.quizz-option:disabled {
    cursor: default;
}

.quizz-feedback {
    background: rgba(99, 102, 241, 0.1);
    border-left: 4px solid var(--accent-color);
    padding: 16px;
    border-radius: 4px 8px 8px 4px;
    margin-bottom: 24px;
    animation: fadeIn 0.3s ease;
}

.quizz-footer {
    display: flex;
    justify-content: flex-end;
}

/* Add Quizz Modal */
.modal {
    position: fixed; top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(0,0,0,0.6);
    display: flex; justify-content: center; align-items: center;
    z-index: 1000;
}
.modal.hidden { display: none; }
.modal-content {
    background: var(--bg-color);
    padding: 32px;
    border-radius: 16px;
    width: 90%; max-width: 500px;
    box-shadow: var(--shadow);
    border: 1px solid var(--surface-border);
    position: relative;
    max-height: 90vh;
    overflow-y: auto;
}
.close-modal {
    position: absolute; right: 16px; top: 16px;
    font-size: 28px; cursor: pointer; color: var(--text-secondary);
    transition: color 0.2s;
}
.close-modal:hover { color: var(--accent-color); }
.form-group { margin-bottom: 20px; }
.form-group label { display: block; margin-bottom: 8px; font-weight: 600; font-size: 0.9rem; }
.form-group textarea, .form-group input[type="text"] {
    width: 100%; padding: 12px; border: 1px solid var(--surface-border);
    border-radius: 8px; background: var(--surface-color); color: var(--text-primary);
    font-family: inherit; transition: border-color 0.2s, box-shadow 0.2s;
}
.form-group textarea:focus, .form-group input[type="text"]:focus {
    outline: none; border-color: var(--accent-color);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.2);
}
.option-input-row { display: flex; align-items: center; gap: 8px; margin-bottom: 8px; }
.option-input-row input[type="radio"] { cursor: pointer; width: 18px; height: 18px; }

.highlight { background-color: var(--accent-light); color: var(--accent-color); font-weight: bold; border-radius: 4px; padding: 0 4px; }

/* Floating TTS Panel */
.floating-tts {
    position: fixed;
    bottom: 24px;
    right: 24px;
    background: var(--surface-color);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--surface-border);
    border-radius: 16px;
    padding: 0;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.2);
    z-index: 1000;
    width: 300px;
    transition: opacity 0.25s ease, transform 0.25s cubic-bezier(0.4, 0, 0.2, 1);
    opacity: 1;
    user-select: none;
}
.floating-tts.hidden {
    transform: translateY(120%);
    opacity: 0;
    pointer-events: none;
}
.tts-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px 16px;
    border-bottom: 1px solid var(--surface-border);
    cursor: grab;
    border-radius: 16px 16px 0 0;
}
.tts-header:active {
    cursor: grabbing;
}
.tts-title {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.07em;
}
.tts-close-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 1.2rem;
    cursor: pointer;
    line-height: 1;
    padding: 2px 6px;
    border-radius: 4px;
    transition: color 0.15s ease, background 0.15s ease;
}
.tts-close-btn:hover {
    color: var(--text-primary);
    background: rgba(128,128,128,0.1);
}
.tts-controls {
    padding: 14px 16px 16px;
}
.tts-seek-section {
    margin-bottom: 14px;
}
.tts-time-row {
    display: flex;
    justify-content: space-between;
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-bottom: 6px;
    font-variant-numeric: tabular-nums;
}
.tts-seek-bar {
    -webkit-appearance: none;
    appearance: none;
    width: 100%;
    height: 4px;
    border-radius: 2px;
    background: var(--surface-border);
    outline: none;
    cursor: pointer;
    transition: height 0.12s ease;
}
.tts-seek-bar:hover {
    height: 6px;
}
.tts-seek-bar::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 14px;
    height: 14px;
    border-radius: 50%;
    background: var(--accent-color);
    cursor: pointer;
    box-shadow: 0 0 0 2px rgba(99,102,241,0.25);
    transition: transform 0.1s ease;
}
.tts-seek-bar::-webkit-slider-thumb:hover {
    transform: scale(1.25);
}
.tts-seek-bar::-moz-range-thumb {
    width: 14px;
    height: 14px;
    border: none;
    border-radius: 50%;
    background: var(--accent-color);
    cursor: pointer;
}
.tts-playback-row {
    display: flex;
    align-items: center;
    gap: 14px;
}
.tts-play-btn {
    flex-shrink: 0;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    background: var(--accent-color);
    border: none;
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: background 0.2s ease, transform 0.15s ease, box-shadow 0.2s ease;
    box-shadow: 0 4px 12px rgba(99,102,241,0.35);
}
.tts-play-btn:hover {
    background: var(--accent-hover);
    transform: scale(1.07);
    box-shadow: 0 6px 18px rgba(99,102,241,0.45);
}
.tts-play-btn:active {
    transform: scale(0.96);
}
.tts-settings {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 8px;
}
.tts-setting-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
}
.tts-setting-item label {
    font-size: 0.8rem;
    color: var(--text-secondary);
    white-space: nowrap;
    min-width: 44px;
}
.tts-setting-item select {
    background: var(--bg-color);
    color: var(--text-primary);
    border: 1px solid var(--surface-border);
    padding: 4px 8px;
    border-radius: 6px;
    outline: none;
    font-family: inherit;
    font-size: 0.82rem;
    cursor: pointer;
    flex: 1;
    transition: border-color 0.15s ease;
}
.tts-setting-item select:focus {
    border-color: var(--accent-color);
}
.tts-loading {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-top: 12px;
    font-size: 0.82rem;
    color: var(--text-secondary);
}
.tts-loading.hidden { display: none; }
.tts-spinner {
    width: 14px;
    height: 14px;
    border: 2px solid var(--surface-border);
    border-top-color: var(--accent-color);
    border-radius: 50%;
    animation: tts-spin 0.7s linear infinite;
    flex-shrink: 0;
}
@keyframes tts-spin {
    to { transform: rotate(360deg); }
}