:root {
    --bg-primary: #0f0f0f;
    --bg-secondary: #1a1a1a;
    --bg-tertiary: #252525;
    --text-primary: #ffffff;
    --text-secondary: #d0d0d0;
    --text-muted: #999999;
    --accent: #5b9eff;
    --accent-hover: #7bb3ff;
    --accent-light: rgba(91, 158, 255, 0.1);
    --border: #333333;
    --book-bg: #1e1e1e;
    --book-shadow: rgba(0, 0, 0, 0.4);
    --highlight-yellow: rgba(255, 235, 59, 0.4);
    --highlight-blue: rgba(100, 181, 246, 0.4);
    --highlight-green: rgba(129, 199, 132, 0.4);
    --highlight-pink: rgba(240, 98, 146, 0.4);
    --success: #4caf50;
    --warning: #ff9800;
    --error: #f44336;
}

[data-theme="light"] {
    --bg-primary: #fafafa;
    --bg-secondary: #ffffff;
    --bg-tertiary: #f5f5f5;
    --text-primary: #1a1a1a;
    --text-secondary: #2d2d2d;
    --text-muted: #666666;
    --accent: #0066cc;
    --accent-hover: #0052a3;
    --accent-light: rgba(0, 102, 204, 0.1);
    --border: #e0e0e0;
    --book-bg: #ffffff;
    --book-shadow: rgba(0, 0, 0, 0.15);
}

/* Force dark text on book page in light theme */
[data-theme="light"] .book-page {
    color: #1a1a1a;
    background: #ffffff;
}

[data-theme="light"] .book-page * {
    color: inherit;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    overflow-x: hidden;
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* Smooth page transitions */
.page-content {
    animation: fadeIn 0.4s ease-in-out;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

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

/* Sidebar */
.sidebar {
    width: 280px;
    background: var(--bg-secondary);
    border-right: 2px solid var(--border);
    padding: 2rem 1.5rem;
    overflow-y: auto;
    position: fixed;
    height: 100vh;
    z-index: 100;
    box-shadow: 4px 0 20px rgba(0, 0, 0, 0.1);
    transition: all 0.3s ease;
}

.sidebar-header {
    margin-bottom: 2rem;
    padding-bottom: 1.5rem;
    border-bottom: 1px solid var(--border);
}

.logo {
    font-size: 1.75rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--accent), var(--accent-hover));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 0.5rem;
    transition: all 0.3s;
}

.logo:hover {
    transform: scale(1.05);
}

.subtitle {
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.subject-selector-container {
    margin-top: 1.5rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--border);
}

.subject-selector-label {
    display: block;
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-muted);
    margin-bottom: 0.5rem;
    font-weight: 600;
}

.subject-selector {
    width: 100%;
    padding: 0.75rem 1rem;
    background: var(--bg-tertiary);
    border: 2px solid var(--border);
    border-radius: 8px;
    color: var(--text-primary);
    font-size: 0.875rem;
    font-family: 'Inter', sans-serif;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%235b9eff' d='M6 9L1 4h10z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 1rem center;
    padding-right: 2.5rem;
}

.subject-selector:hover {
    border-color: var(--accent);
    background-color: var(--bg-secondary);
}

.subject-selector:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 3px var(--accent-light);
}

.nav-section {
    margin-bottom: 2rem;
}

.nav-section-title {
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-muted);
    margin-bottom: 0.75rem;
    font-weight: 600;
}

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

.nav-item {
    margin-bottom: 0.5rem;
}

.nav-link {
    display: block;
    padding: 0.75rem 1rem;
    color: var(--text-secondary);
    text-decoration: none;
    border-radius: 8px;
    font-size: 0.875rem;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    cursor: pointer;
    position: relative;
    font-weight: 400;
}

.nav-link::before {
    content: '';
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 3px;
    height: 0;
    background: var(--accent);
    border-radius: 0 2px 2px 0;
    transition: height 0.3s ease;
}

.nav-link:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
    padding-left: 1.25rem;
    transform: translateX(4px);
}

.nav-link:hover::before {
    height: 60%;
}

.nav-link.active {
    background: linear-gradient(90deg, var(--accent-light), transparent);
    color: var(--accent);
    font-weight: 600;
    padding-left: 1.25rem;
    border-left: 3px solid var(--accent);
}

.nav-link.active::before {
    height: 100%;
}

.sidebar-footer {
    margin-top: 2rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--border);
}

.btn-contact {
    width: 100%;
    padding: 0.875rem 1rem;
    background: var(--bg-tertiary);
    border: 2px solid var(--border);
    border-radius: 10px;
    color: var(--text-primary);
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    align-items: center;
    gap: 0.5rem;
    justify-content: center;
    position: relative;
    overflow: hidden;
}

.btn-contact::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: var(--accent);
    transform: translate(-50%, -50%);
    transition: width 0.6s, height 0.6s;
    z-index: 0;
}

.btn-contact span,
.btn-contact {
    position: relative;
    z-index: 1;
}

.btn-contact:hover {
    border-color: var(--accent);
    color: white;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(91, 158, 255, 0.3);
}

.btn-contact:hover::before {
    width: 300px;
    height: 300px;
}

.btn-contact:active {
    transform: translateY(0);
}

/* Main Content */
.main-content {
    flex: 1;
    margin-left: 280px;
    padding: 2rem;
    display: flex;
    justify-content: center;
    min-height: 100vh;
}

.book-container {
    width: 100%;
    max-width: 900px;
}

.book-page {
    background: var(--book-bg);
    border-radius: 16px;
    box-shadow: 0 20px 60px var(--book-shadow), 0 0 0 1px var(--border);
    padding: 3rem 4rem;
    min-height: calc(100vh - 4rem);
    position: relative;
    border: 1px solid var(--border);
    transition: all 0.3s ease;
    animation: slideIn 0.4s ease-out;
    color: var(--text-primary);
}

/* Ensure book page has correct background in dark theme */
:root .book-page {
    background: #1e1e1e;
    color: #ffffff;
}

/* Dark theme: white text on dark book */
:root .book-page {
    color: #ffffff;
    background: #1e1e1e;
}

/* Light theme: dark text on white book */
[data-theme="light"] .book-page {
    color: #1a1a1a;
    background: #ffffff;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: scale(0.98);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

.book-page:hover {
    box-shadow: 0 25px 70px var(--book-shadow), 0 0 0 1px var(--accent-light);
}

.page-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border);
}

.btn-back {
    background: var(--bg-tertiary);
    border: 2px solid var(--border);
    color: var(--text-primary);
    padding: 0.625rem 1.25rem;
    border-radius: 10px;
    cursor: pointer;
    font-size: 0.875rem;
    font-weight: 500;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    align-items: center;
    gap: 0.5rem;
    position: relative;
    overflow: hidden;
}

.btn-back::before {
    content: '';
    position: absolute;
    left: -100%;
    top: 0;
    width: 100%;
    height: 100%;
    background: var(--accent);
    transition: left 0.3s;
    z-index: 0;
}

.btn-back span {
    position: relative;
    z-index: 1;
}

.btn-back:hover {
    border-color: var(--accent);
    color: white;
    transform: translateX(-4px);
    box-shadow: 0 4px 12px rgba(91, 158, 255, 0.3);
}

.btn-back:hover::before {
    left: 0;
}

.page-actions {
    display: flex;
    gap: 0.5rem;
}

.btn-action {
    background: transparent;
    border: 2px solid var(--border);
    color: var(--text-primary);
    padding: 0.5rem;
    border-radius: 10px;
    cursor: pointer;
    font-size: 1.125rem;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.btn-action::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: var(--accent-light);
    transform: translate(-50%, -50%);
    transition: width 0.4s, height 0.4s;
}

.btn-action:hover {
    background: var(--bg-tertiary);
    border-color: var(--accent);
    transform: scale(1.1) rotate(5deg);
    box-shadow: 0 4px 12px rgba(91, 158, 255, 0.3);
}

.btn-action:hover::before {
    width: 100%;
    height: 100%;
}

.btn-action:active {
    transform: scale(1.05) rotate(0deg);
}

/* Page Content */
.page-content {
    color: var(--text-primary);
    font-size: 1.0625rem;
    line-height: 1.8;
}

/* Ensure text is dark on light book background */
[data-theme="light"] .book-page .page-content {
    color: #1a1a1a;
}

[data-theme="light"] .book-page .page-content p,
[data-theme="light"] .book-page .page-content li,
[data-theme="light"] .book-page .page-content td {
    color: #2d2d2d;
}

[data-theme="light"] .book-page .page-content h1,
[data-theme="light"] .book-page .page-content h2,
[data-theme="light"] .book-page .page-content h3,
[data-theme="light"] .book-page .page-content h4 {
    color: #1a1a1a;
}

/* Ensure dark theme has dark background and white text */
:root .book-page .page-content {
    color: #ffffff;
}

:root .book-page .page-content p,
:root .book-page .page-content li,
:root .book-page .page-content td {
    color: #d0d0d0;
}

:root .book-page .page-content h1,
:root .book-page .page-content h2,
:root .book-page .page-content h3,
:root .book-page .page-content h4 {
    color: #ffffff;
}

.page-content h1 {
    font-size: 2.75rem;
    font-weight: 800;
    margin-bottom: 1.5rem;
    color: inherit;
    border-bottom: 4px solid var(--accent);
    padding-bottom: 0.75rem;
    letter-spacing: -0.02em;
    line-height: 1.2;
}

.page-content h2 {
    font-size: 2rem;
    font-weight: 700;
    margin-top: 3rem;
    margin-bottom: 1.25rem;
    color: inherit;
    position: relative;
    padding-left: 1rem;
    border-left: 4px solid var(--accent);
}

.page-content h3 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-top: 2.5rem;
    margin-bottom: 1rem;
    color: inherit;
    position: relative;
}

.page-content h3::before {
    content: '▸';
    color: var(--accent);
    margin-right: 0.5rem;
    font-size: 1.2rem;
}

.page-content h4 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-top: 2rem;
    margin-bottom: 0.75rem;
    color: inherit;
}

.page-content p {
    margin-bottom: 1.5rem;
    color: inherit;
    font-size: 1.0625rem;
    line-height: 1.9;
    letter-spacing: 0.01em;
}

.page-content ul,
.page-content ol {
    margin-bottom: 1.5rem;
    padding-left: 2rem;
}

.page-content li {
    margin-bottom: 0.875rem;
    color: inherit;
    line-height: 1.8;
    position: relative;
    padding-left: 0.5rem;
}

.page-content ul li::marker {
    color: var(--accent);
    font-weight: 600;
}

.page-content ol li::marker {
    color: var(--accent);
    font-weight: 600;
}

.page-content code {
    font-family: 'JetBrains Mono', 'Courier New', monospace;
    background: var(--bg-tertiary);
    padding: 0.25rem 0.5rem;
    border-radius: 6px;
    font-size: 0.9em;
    color: var(--accent);
    font-weight: 500;
    border: 1px solid var(--border);
    transition: all 0.2s;
}

.page-content code:hover {
    background: var(--accent-light);
    border-color: var(--accent);
}

.page-content pre {
    background: var(--bg-secondary);
    border: 2px solid var(--border);
    border-left: 4px solid var(--accent);
    border-radius: 12px;
    padding: 1.5rem;
    overflow-x: auto;
    margin-bottom: 2rem;
    font-family: 'JetBrains Mono', 'Courier New', monospace;
    font-size: 0.9rem;
    line-height: 1.7;
    position: relative;
    transition: all 0.3s;
}

.page-content pre:hover {
    border-color: var(--accent);
    box-shadow: 0 4px 16px rgba(91, 158, 255, 0.1);
}

.page-content pre code {
    background: transparent;
    padding: 0;
    color: var(--text-primary);
}

.page-content blockquote {
    border-left: 4px solid var(--accent);
    padding: 1rem 1.5rem;
    margin: 2rem 0;
    color: inherit;
    font-style: italic;
    background: var(--accent-light);
    border-radius: 0 8px 8px 0;
    position: relative;
}

.page-content blockquote::before {
    content: '"';
    font-size: 4rem;
    color: var(--accent);
    opacity: 0.3;
    position: absolute;
    left: 0.5rem;
    top: -0.5rem;
    font-family: Georgia, serif;
}

.page-content table {
    width: 100%;
    border-collapse: separate;
    border-spacing: 0;
    margin: 2rem 0;
    border-radius: 12px;
    overflow: hidden;
    border: 2px solid var(--border);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.page-content table th,
.page-content table td {
    padding: 1rem;
    border-bottom: 1px solid var(--border);
    text-align: left;
    transition: background 0.2s;
}

.page-content table th {
    background: var(--bg-tertiary);
    font-weight: 600;
    color: var(--text-primary);
    text-transform: uppercase;
    font-size: 0.875rem;
    letter-spacing: 0.05em;
}

.page-content table td {
    color: inherit;
}

.page-content table tbody tr:hover {
    background: var(--accent-light);
}

.page-content table tbody tr:last-child td {
    border-bottom: none;
}

.page-content hr {
    border: none;
    border-top: 2px solid var(--border);
    margin: 3rem 0;
    position: relative;
}

.page-content hr::after {
    content: '◆';
    position: absolute;
    top: -10px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--book-bg);
    padding: 0 1rem;
    color: var(--accent);
    font-size: 1.2rem;
}

.page-content strong {
    color: inherit;
    font-weight: 700;
    background: var(--accent-light);
    padding: 0.1rem 0.3rem;
    border-radius: 4px;
}

.page-content em {
    color: inherit;
    font-style: italic;
    font-weight: 500;
}

/* Links in page content - better visibility */
.page-content a {
    color: #7bb3ff; /* Lighter blue for better visibility */
    text-decoration: none;
    border-bottom: 1px solid rgba(123, 179, 255, 0.3);
    transition: all 0.2s ease;
    font-weight: 500;
}

.page-content a:hover {
    color: #9cc5ff; /* Even lighter on hover */
    border-bottom-color: #7bb3ff;
    border-bottom-width: 2px;
}

/* Light theme link colors */
[data-theme="light"] .page-content a {
    color: #0066cc; /* Darker blue for light theme */
    border-bottom-color: rgba(0, 102, 204, 0.3);
}

[data-theme="light"] .page-content a:hover {
    color: #0052a3; /* Darker on hover for light theme */
    border-bottom-color: #0066cc;
}

/* Welcome Screen */
.welcome-screen {
    text-align: center;
    padding: 3rem 0;
}

.welcome-screen h1 {
    font-size: 3.5rem;
    margin-bottom: 1rem;
    border: none;
    padding: 0;
    background: linear-gradient(135deg, var(--accent), var(--accent-hover));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    font-weight: 800;
    letter-spacing: -0.02em;
}

.lead {
    font-size: 1.375rem;
    color: inherit;
    margin-bottom: 3rem;
    font-weight: 400;
    letter-spacing: 0.01em;
}

.welcome-features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin: 3rem 0;
}

.feature-card {
    background: var(--bg-secondary);
    border: 2px solid var(--border);
    border-radius: 16px;
    padding: 2rem;
    text-align: left;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.feature-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, var(--accent-light), transparent);
    transition: left 0.5s;
}

.feature-card:hover {
    transform: translateY(-6px) scale(1.02);
    border-color: var(--accent);
    box-shadow: 0 12px 32px rgba(91, 158, 255, 0.2);
}

.feature-card:hover::before {
    left: 100%;
}

.feature-card h3 {
    font-size: 1.25rem;
    margin-bottom: 0.75rem;
    margin-top: 0;
}

.feature-card p {
    color: var(--text-secondary);
    margin: 0;
}

[data-theme="light"] .feature-card p {
    color: #4a4a4a;
}

.quick-start {
    margin-top: 3rem;
    padding: 2rem;
    background: var(--bg-secondary);
    border-radius: 12px;
    border: 1px solid var(--border);
}

.quick-start h3 {
    margin-top: 0;
    margin-bottom: 0.5rem;
}

.quick-start p {
    color: var(--text-secondary);
    margin: 0;
}

[data-theme="light"] .quick-start p {
    color: #4a4a4a;
}

/* Subject Cards */
.subjects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin: 3rem 0;
}

.subject-card {
    background: var(--bg-secondary);
    border: 2px solid var(--border);
    border-radius: 16px;
    padding: 2rem;
    text-align: center;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.subject-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, var(--accent-light), transparent);
    transition: left 0.5s;
}

.subject-card:hover {
    transform: translateY(-6px) scale(1.02);
    border-color: var(--accent);
    box-shadow: 0 12px 32px rgba(91, 158, 255, 0.2);
}

.subject-card:hover::before {
    left: 100%;
}

.subject-icon {
    font-size: 3rem;
    margin-bottom: 1rem;
}

.subject-card h3 {
    font-size: 1.5rem;
    margin-bottom: 0.5rem;
    margin-top: 0;
    color: var(--text-primary);
}

.subject-card p {
    color: var(--text-secondary);
    margin-bottom: 1rem;
    font-size: 0.875rem;
}

.subject-stats {
    font-size: 0.75rem;
    color: var(--text-muted);
    padding: 0.5rem 1rem;
    background: var(--bg-tertiary);
    border-radius: 20px;
    display: inline-block;
}

/* Welcome Sections */
.welcome-section {
    margin: 2rem 0;
    padding: 1.5rem;
    background: var(--bg-secondary);
    border-radius: 12px;
    border: 1px solid var(--border);
}

.welcome-section h3 {
    margin-top: 0;
    margin-bottom: 1rem;
    font-size: 1.25rem;
    color: var(--accent);
    border-left: 4px solid var(--accent);
    padding-left: 1rem;
}

.welcome-notes-list {
    list-style: none;
    padding: 0;
    margin: 0;
}

.welcome-note-item {
    margin-bottom: 0.5rem;
}

.welcome-note-link {
    display: block;
    padding: 0.75rem 1rem;
    color: var(--text-secondary);
    text-decoration: none;
    border-radius: 8px;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    border-left: 3px solid transparent;
}

.welcome-note-link:hover {
    background: var(--bg-tertiary);
    color: var(--accent);
    border-left-color: var(--accent);
    transform: translateX(4px);
}

/* Page Footer */
.page-footer {
    margin-top: 3rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--border);
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 1rem;
}

.page-info {
    color: var(--text-primary);
    font-size: 0.875rem;
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.page-info::before {
    content: '📄';
    font-size: 1rem;
}

.page-controls {
    display: flex;
    gap: 0.75rem;
}

.btn-nav {
    background: var(--bg-tertiary);
    border: 2px solid var(--border);
    color: var(--text-primary);
    padding: 0.75rem 1.5rem;
    border-radius: 10px;
    cursor: pointer;
    font-size: 0.875rem;
    font-weight: 500;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
}

.btn-nav::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: var(--accent);
    transform: translate(-50%, -50%);
    transition: width 0.5s, height 0.5s;
    z-index: 0;
}

.btn-nav span {
    position: relative;
    z-index: 1;
}

.btn-nav:hover:not(:disabled) {
    border-color: var(--accent);
    color: white;
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(91, 158, 255, 0.3);
}

.btn-nav:hover:not(:disabled)::before {
    width: 300px;
    height: 300px;
}

.btn-nav:active:not(:disabled) {
    transform: translateY(0);
}

.btn-nav:disabled {
    opacity: 0.4;
    cursor: not-allowed;
    background: var(--bg-secondary);
}

/* Highlighting */
.highlight-mode .page-content {
    user-select: text;
    -webkit-user-select: text;
    -moz-user-select: text;
    -ms-user-select: text;
    touch-action: pan-y;
}

/* Ensure text is selectable on mobile */
.highlight-mode .page-content * {
    -webkit-touch-callout: default;
    -webkit-user-select: text;
    user-select: text;
}

.highlight {
    position: relative;
    padding: 2px 6px;
    border-radius: 4px;
    cursor: pointer;
    transition: all 0.2s;
    font-weight: 500;
}

.highlight:hover {
    transform: scale(1.05);
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.2);
}

.highlight-yellow {
    background: var(--highlight-yellow);
    border-bottom: 2px solid #fbc02d;
}

.highlight-blue {
    background: var(--highlight-blue);
    border-bottom: 2px solid #64b5f6;
}

.highlight-green {
    background: var(--highlight-green);
    border-bottom: 2px solid #81c784;
}

.highlight-pink {
    background: var(--highlight-pink);
    border-bottom: 2px solid #f06292;
}

/* Highlight Tooltip */
.highlight-tooltip {
    position: fixed;
    background: var(--bg-secondary);
    border: 2px solid var(--accent);
    border-radius: 12px;
    padding: 0.75rem;
    display: flex;
    gap: 0.75rem;
    z-index: 10000;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
    backdrop-filter: blur(10px);
}

/* Mobile optimizations for tooltip */
@media (max-width: 768px) {
    .highlight-tooltip {
        padding: 1rem;
        gap: 1rem;
        border-radius: 16px;
        box-shadow: 0 12px 32px rgba(0, 0, 0, 0.5);
    }
}

.tooltip-btn {
    background: var(--bg-secondary);
    border: 2px solid var(--border);
    border-radius: 8px;
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    font-size: 1.125rem;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
    -webkit-tap-highlight-color: transparent;
    touch-action: manipulation;
}

/* Mobile: Larger buttons for easier tapping */
@media (max-width: 768px) {
    .tooltip-btn {
        width: 44px;
        height: 44px;
        font-size: 1.25rem;
        border-radius: 10px;
    }
}

.tooltip-btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: var(--accent-light);
    transform: translate(-50%, -50%);
    transition: width 0.3s, height 0.3s;
}

.tooltip-btn:hover {
    background: var(--bg-tertiary);
    border-color: var(--accent);
    transform: scale(1.15) rotate(5deg);
    box-shadow: 0 4px 12px rgba(91, 158, 255, 0.3);
}

.tooltip-btn:hover::before {
    width: 100%;
    height: 100%;
}

.tooltip-btn:active {
    transform: scale(1.05) rotate(0deg);
}

.tooltip-btn[data-color="remove"] {
    font-size: 0.875rem;
}

/* Responsive */
@media (max-width: 1024px) {
    .sidebar {
        width: 240px;
    }
    
    .main-content {
        margin-left: 240px;
    }
    
    .book-page {
        padding: 2rem 3rem;
    }
}

@media (max-width: 768px) {
    .sidebar {
        transform: translateX(-100%);
        transition: transform 0.3s;
    }
    
    .sidebar.open {
        transform: translateX(0);
    }
    
    .main-content {
        margin-left: 0;
        padding: 1rem;
    }
    
    .book-page {
        padding: 1.5rem 2rem;
    }
    
    .page-content h1 {
        font-size: 2rem;
    }
    
    .welcome-features {
        grid-template-columns: 1fr;
    }
}

/* Error Styles */
.error {
    padding: 2rem;
    text-align: center;
}

.error h2 {
    color: #ff6b6b;
    margin-bottom: 1rem;
    border: none;
    padding: 0;
}

.error p {
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
}

.error code {
    background: var(--bg-tertiary);
    padding: 0.2rem 0.4rem;
    border-radius: 4px;
    font-size: 0.9em;
    color: var(--accent);
}

/* Print Styles */
@media print {
    .sidebar,
    .page-header,
    .page-footer,
    .highlight-tooltip {
        display: none;
    }
    
    .main-content {
        margin-left: 0;
        padding: 0;
    }
    
    .book-page {
        box-shadow: none;
        border: none;
        padding: 0;
    }
}

/* Loading Animation */
@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Scrollbar */
::-webkit-scrollbar {
    width: 10px;
    height: 10px;
}

::-webkit-scrollbar-track {
    background: var(--bg-secondary);
    border-radius: 5px;
}

::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 5px;
    border: 2px solid var(--bg-secondary);
}

::-webkit-scrollbar-thumb:hover {
    background: var(--accent);
}

/* Contact Modal/Chatbox */
.contact-modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 10000;
    display: flex;
    align-items: center;
    justify-content: center;
    animation: fadeIn 0.3s ease;
}

.contact-modal-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.7);
    backdrop-filter: blur(4px);
}

.contact-modal-content {
    position: relative;
    background: var(--bg-secondary);
    border: 2px solid var(--border);
    border-radius: 16px;
    width: 90%;
    max-width: 500px;
    max-height: 90vh;
    overflow-y: auto;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
    animation: slideUp 0.3s ease;
    z-index: 10001;
}

@keyframes slideUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.contact-modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.5rem 2rem;
    border-bottom: 1px solid var(--border);
}

.contact-modal-header h2 {
    margin: 0;
    font-size: 1.5rem;
    color: var(--text-primary);
    font-weight: 600;
}

.contact-modal-close {
    background: transparent;
    border: 2px solid var(--border);
    color: var(--text-secondary);
    width: 36px;
    height: 36px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 1.25rem;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.contact-modal-close:hover {
    background: var(--bg-tertiary);
    border-color: var(--accent);
    color: var(--accent);
    transform: rotate(90deg);
}

.contact-form {
    padding: 2rem;
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
    font-size: 0.875rem;
    font-weight: 500;
}

.form-group input,
.form-group textarea {
    width: 100%;
    padding: 0.875rem 1rem;
    background: var(--bg-tertiary);
    border: 2px solid var(--border);
    border-radius: 8px;
    color: var(--text-primary);
    font-size: 0.875rem;
    font-family: 'Inter', sans-serif;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    box-sizing: border-box;
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 3px var(--accent-light);
}

.form-group textarea {
    resize: vertical;
    min-height: 120px;
}

.form-actions {
    margin-top: 2rem;
}

.btn-submit {
    width: 100%;
    padding: 0.875rem 1.5rem;
    background: var(--accent);
    border: 2px solid var(--accent);
    border-radius: 10px;
    color: white;
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    position: relative;
    overflow: hidden;
}

.btn-submit:hover:not(:disabled) {
    background: var(--accent-hover);
    border-color: var(--accent-hover);
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(91, 158, 255, 0.4);
}

.btn-submit:active:not(:disabled) {
    transform: translateY(0);
}

.btn-submit:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

.btn-loader {
    animation: spin 1s linear infinite;
}

.form-message {
    margin-top: 1rem;
    padding: 1rem;
    border-radius: 8px;
    font-size: 0.875rem;
    text-align: center;
}

.form-message.success {
    background: rgba(76, 175, 80, 0.1);
    border: 2px solid #4caf50;
    color: #4caf50;
}

.form-message.error {
    background: rgba(244, 67, 54, 0.1);
    border: 2px solid #f44336;
    color: #f44336;
}

/* Mobile optimizations for contact modal */
@media (max-width: 768px) {
    .contact-modal-content {
        width: 95%;
        max-height: 95vh;
    }
    
    .contact-modal-header {
        padding: 1rem 1.5rem;
    }
    
    .contact-form {
        padding: 1.5rem;
    }
    
    .contact-modal-header h2 {
        font-size: 1.25rem;
    }
}