/* Visual & Accessible Design System */

/* Variables */
:root {
    --primary-color: #0066cc;
    --primary-light: #e6f0fa;
    --secondary-color: #10b981;
    --accent-color: #f59e0b;
    --danger-color: #ef4444;
    --text-color: #1f2937;
    --text-muted: #6b7280;
    --bg-color: #f9fafb;
    --card-bg: #ffffff;
    --border-color: #e5e7eb;
    --sidebar-width: 280px;
    --sidebar-bg: #ffffff;
    --code-bg: #1e1e1e;
    --code-text: #d4d4d4;
    --code-keyword: #569cd6;
    --code-string: #ce9178;
    --code-number: #b5cea8;
    --code-comment: #6a9955;
    --code-function: #dcdcaa;
    --code-class: #4ec9b0;
    --code-variable: #9cdcfe;
    --code-operator: #d4d4d4;
    --code-builtin: #4ec9b0;
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
    --shadow-md: 0 4px 6px rgba(0,0,0,0.07);
    --shadow-lg: 0 10px 15px rgba(0,0,0,0.1);
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
}

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

html, body {
    height: auto;
    min-height: 100%;
}

/* Main Layout */
.main-layout {
    display: flex;
    height: 100vh;
    width: 100vw;
    background: var(--bg-color);
}

/* Sidebar */
.sidebar {
    width: var(--sidebar-width);
    background: var(--sidebar-bg);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    flex-shrink: 0;
    overflow-y: auto;
}

.sidebar-header {
    padding: 1.5rem;
    border-bottom: 1px solid var(--border-color);
    background: linear-gradient(135deg, var(--primary-color) 0%, #3b82f6 100%);
}

.sidebar-header .logo {
    font-size: 1.5rem;
    font-weight: 800;
    color: white;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.sidebar-nav {
    flex: 1;
    padding: 1rem 0;
}

.nav-tree {
    list-style: none;
    padding: 0;
    margin: 0;
}

.nav-item {
    margin: 0.25rem 0.5rem;
}

.nav-link {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    padding: 0.75rem 1rem;
    color: var(--text-muted);
    text-decoration: none;
    border-radius: var(--radius-sm);
    font-weight: 500;
    transition: all 0.2s ease;
}

.nav-link:hover {
    background: var(--primary-light);
    color: var(--primary-color);
}

.nav-link.active {
    background: linear-gradient(90deg, var(--primary-light) 0%, #ffffff 100%);
    color: var(--primary-color);
    font-weight: 700;
    border-left: 4px solid var(--primary-color);
    box-shadow: inset 2px 0 8px rgba(0, 102, 204, 0.15);
    position: relative;
}

.nav-link.active::before {
    content: '▶';
    position: absolute;
    left: 8px;
    font-size: 0.6rem;
    color: var(--primary-color);
}

.nav-icon {
    font-size: 1.25rem;
    width: 28px;
    text-align: center;
}

.nav-text {
    font-size: 0.9rem;
}

/* Content Area */
.content-area {
    flex: 1;
    overflow: hidden;
    background: var(--bg-color);
}

.content-frame {
    width: 100%;
    height: 100%;
    border: none;
    background: var(--bg-color);
    overflow-y: auto;
    overflow-x: hidden;
}

.content-frame body {
    padding: 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Segoe UI', sans-serif;
    line-height: 1.7;
    color: var(--text-color);
    background: var(--bg-color);
    min-height: auto;
}

/* Container */
.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 0 24px;
}

/* Sections */
.section {
    padding: 3rem 0;
    min-height: auto;
    background: var(--bg-color);
}

.content-frame .section {
    padding: 2rem;
}

/* Section Title */
.section-title {
    font-size: 2rem;
    text-align: center;
    margin-bottom: 0.5rem;
    color: var(--text-color);
    font-weight: 700;
}

.section-subtitle {
    text-align: center;
    color: var(--text-muted);
    font-size: 1.1rem;
    margin-bottom: 2.5rem;
}

/* Cards Grid */
.cards-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
    margin-bottom: 2rem;
}

.card-grid-3 {
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
}

.card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.5rem;
    transition: all 0.3s ease;
    box-shadow: var(--shadow-sm);
}

.card:hover {
    box-shadow: var(--shadow-md);
    transform: translateY(-2px);
}

.card-header {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-bottom: 1rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border-color);
}

.card-icon {
    font-size: 2rem;
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--primary-light);
    border-radius: var(--radius-sm);
}

.card-title {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-color);
}

.card-subtitle {
    font-size: 0.85rem;
    color: var(--text-muted);
}

.card-body {
    color: var(--text-muted);
    font-size: 0.95rem;
}

.card-body p {
    margin-bottom: 0.75rem;
}

.card-body ul {
    padding-left: 1.25rem;
    margin: 0.75rem 0;
}

.card-body li {
    margin-bottom: 0.5rem;
}

/* Level Card */
.level-card {
    border-left: 4px solid var(--primary-color);
}

.level-card.level-1 { border-left-color: var(--secondary-color); }
.level-card.level-2 { border-left-color: var(--accent-color); }
.level-card.level-3 { border-left-color: var(--primary-color); }

.level-badge {
    display: inline-flex;
    align-items: center;
    gap: 0.25rem;
    background: var(--primary-light);
    color: var(--primary-color);
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 600;
    margin-bottom: 0.75rem;
}

/* Tables */
.table-container {
    overflow-x: auto;
    margin: 1.5rem 0;
    background: var(--card-bg);
    border-radius: var(--radius-md);
    border: 1px solid var(--border-color);
}

table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.9rem;
}

th, td {
    padding: 0.875rem 1rem;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

th {
    background: var(--bg-color);
    font-weight: 600;
    color: var(--text-color);
}

tr:hover td {
    background: var(--primary-light);
}

tr:last-child td {
    border-bottom: none;
}

/* Diagram Box */
.diagram-box {
    background: var(--card-bg);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.5rem;
    margin: 1.5rem 0;
    text-align: center;
}

.diagram-title {
    font-weight: 600;
    color: var(--text-color);
    margin-bottom: 1rem;
}

.diagram-content {
    font-family: 'Courier New', monospace;
    font-size: 0.85rem;
    line-height: 1.6;
    color: var(--text-color);
    white-space: pre;
    overflow-x: auto;
}

/* Info Box */
.info-box {
    padding: 1rem 1.25rem;
    border-radius: var(--radius-sm);
    margin: 1rem 0;
    border-left: 4px solid;
}

.info-box.tip {
    background: #ecfdf5;
    border-color: var(--secondary-color);
}

.info-box.warning {
    background: #fffbeb;
    border-color: var(--accent-color);
}

.info-box.info {
    background: var(--primary-light);
    border-color: var(--primary-color);
}

.info-box.danger {
    background: #fef2f2;
    border-color: var(--danger-color);
}

.info-box-title {
    font-weight: 600;
    margin-bottom: 0.5rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

/* Step Box */
.step-box {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    margin: 1.5rem 0;
    overflow: hidden;
}

.step-header {
    background: var(--primary-color);
    color: white;
    padding: 0.75rem 1.25rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.step-number {
    width: 28px;
    height: 28px;
    background: rgba(255,255,255,0.2);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
}

.step-content {
    padding: 1.25rem;
}

/* Comparison Table */
.comparison-row {
    display: grid;
    grid-template-columns: 150px 1fr 1fr;
    gap: 1px;
    background: var(--border-color);
    border-radius: var(--radius-sm);
    overflow: hidden;
    margin: 0.5rem 0;
}

.comparison-header {
    background: var(--bg-color);
    font-weight: 600;
    padding: 0.75rem 1rem;
}

.comparison-cell {
    background: var(--card-bg);
    padding: 0.75rem 1rem;
}

/* Timeline */
.timeline {
    position: relative;
    padding-left: 2rem;
    margin: 1.5rem 0;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 7px;
    top: 0;
    bottom: 0;
    width: 2px;
    background: var(--border-color);
}

.timeline-item {
    position: relative;
    padding-bottom: 1.5rem;
}

.timeline-item::before {
    content: '';
    position: absolute;
    left: -2rem;
    top: 4px;
    width: 12px;
    height: 12px;
    background: var(--primary-color);
    border-radius: 50%;
    border: 2px solid white;
}

.timeline-date {
    font-size: 0.8rem;
    color: var(--text-muted);
    font-weight: 600;
    margin-bottom: 0.25rem;
}

.timeline-title {
    font-weight: 600;
    color: var(--text-color);
    margin-bottom: 0.5rem;
}

.timeline-desc {
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* Tags */
.tags {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    margin-top: 0.75rem;
}

.tag {
    background: var(--primary-light);
    color: var(--primary-color);
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.8rem;
    font-weight: 500;
}

.tag.green { background: #ecfdf5; color: #059669; }
.tag.yellow { background: #fffbeb; color: #d97706; }
.tag.red { background: #fef2f2; color: #dc2626; }
.tag.gray { background: #f3f4f6; color: #6b7280; }

/* Code Section */
.code-sections {
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

.code-section {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    overflow: hidden;
}

.code-header {
    background: #f8fafc;
    padding: 1rem 1.25rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--border-color);
}

.code-header h3 {
    margin: 0;
    color: var(--text-color);
    font-size: 1rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.code-block {
    margin: 0;
    padding: 1.25rem;
    background: var(--code-bg);
    overflow-x: auto;
    font-family: 'Fira Code', 'Monaco', 'Consolas', 'Courier New', monospace;
    font-size: 0.9rem;
    line-height: 1.8;
    color: var(--code-text);
    position: relative;
    white-space: pre;
    word-wrap: normal;
    border-radius: var(--radius-sm);
}

.code-block code {
    font-family: inherit;
    font-size: inherit;
    line-height: inherit;
    display: block;
    white-space: pre;
    overflow-x: auto;
}

/* Python Syntax Highlighting */
.code-block code .token.keyword { color: var(--code-keyword); font-weight: 500; }
.code-block code .token.string { color: var(--code-string); }
.code-block code .token.number { color: var(--code-number); }
.code-block code .token.comment { color: var(--code-comment); font-style: italic; }
.code-block code .token.function { color: var(--code-function); }
.code-block code .token.class { color: var(--code-class); }
.code-block code .token.variable { color: var(--code-variable); }
.code-block code .token.operator { color: var(--code-operator); }
.code-block code .token.builtin { color: var(--code-builtin); }
.code-block code .def { color: var(--code-function); font-weight: 500; }
.code-block code .param { color: var(--code-variable); }
.code-block code .decorator { color: var(--code-keyword); }
.code-block code .annotation { color: var(--code-keyword); }

/* Concept Cards */
.concept-card {
    display: flex;
    gap: 1rem;
    padding: 1rem;
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    margin-bottom: 0.75rem;
}

.concept-icon {
    font-size: 1.5rem;
    flex-shrink: 0;
}

.concept-content h4 {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text-color);
    margin-bottom: 0.25rem;
}

.concept-content p {
    font-size: 0.85rem;
    color: var(--text-muted);
    margin: 0;
}

/* Flow Chart */
.flow-chart {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.5rem;
    padding: 1.5rem;
}

.flow-item {
    background: var(--card-bg);
    border: 2px solid var(--primary-color);
    border-radius: var(--radius-sm);
    padding: 0.75rem 1.5rem;
    font-weight: 500;
    text-align: center;
    min-width: 200px;
}

.flow-arrow {
    font-size: 1.25rem;
    color: var(--primary-color);
}

.flow-item.start {
    background: var(--primary-color);
    color: white;
    border-radius: 25px;
}

.flow-item.end {
    background: var(--secondary-color);
    color: white;
    border-radius: 25px;
    border-color: var(--secondary-color);
}

/* Horizontal Flow */
.flow-horizontal {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 1.5rem;
}

.flow-h-item {
    background: var(--card-bg);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 0.75rem 1rem;
    text-align: center;
    min-width: 120px;
}

.flow-h-arrow {
    color: var(--text-muted);
    font-size: 1.25rem;
}

.flow-h-item.start {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
    border-radius: 25px;
}

.flow-h-item.end {
    background: var(--secondary-color);
    color: white;
    border-color: var(--secondary-color);
    border-radius: 25px;
}

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

::-webkit-scrollbar-track {
    background: #e5e7eb;
    border-radius: 4px;
}

::-webkit-scrollbar-thumb {
    background: #c1c4c8;
    border-radius: 4px;
}

.code-block::-webkit-scrollbar {
    height: 6px;
}

/* Footer */
.footer {
    background: var(--card-bg);
    border-top: 1px solid var(--border-color);
    padding: 2rem 0;
    text-align: center;
    margin-top: 3rem;
}

.footer p {
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* Responsive */
@media (max-width: 768px) {
    .main-layout {
        flex-direction: column;
    }

    .sidebar {
        width: 100%;
        height: auto;
        max-height: 300px;
    }

    .cards-grid {
        grid-template-columns: 1fr;
    }

    .card-grid-3 {
        grid-template-columns: 1fr;
    }

    .comparison-row {
        grid-template-columns: 1fr;
    }

    .comparison-header {
        display: none;
    }

    .section-title {
        font-size: 1.5rem;
    }

    .container {
        padding: 0 16px;
    }

    .flow-horizontal {
        flex-direction: column;
    }

    .flow-h-arrow {
        transform: rotate(90deg);
    }
}

/* Print Styles */
@media print {
    .sidebar {
        display: none;
    }

    .content-area {
        overflow: visible;
    }

    .content-frame {
        height: auto;
        overflow: visible;
    }
}

/* Collapsible Details */
details {
    background: var(--card-bg);
    border-radius: 8px;
    border: 1px solid var(--border-color);
    margin-bottom: 1rem;
}

details[open] {
    box-shadow: var(--shadow-sm);
}

summary {
    padding: 1rem;
    cursor: pointer;
    font-weight: 600;
    color: var(--text-primary);
    list-style: none;
    display: flex;
    align-items: center;
    justify-content: space-between;
    border-radius: 8px;
    transition: background var(--transition-fast);
}

summary:hover {
    background: var(--bg-secondary);
}

summary::-webkit-details-marker {
    display: none;
}

summary::after {
    content: '▼';
    font-size: 0.75rem;
    color: var(--text-secondary);
    transition: transform var(--transition-fast);
}

details[open] summary::after {
    transform: rotate(180deg);
}

details .details-content {
    padding: 0 1rem 1rem 1rem;
    border-top: 1px solid var(--border-color);
    margin-top: 0;
    padding-top: 1rem;
}

/* Collapsible code blocks */
details code {
    background: var(--bg-secondary);
    padding: 0.125rem 0.375rem;
    border-radius: 4px;
    font-family: 'SF Mono', Consolas, 'Liberation Mono', Menlo, monospace;
    font-size: 0.875em;
}

details pre {
    margin: 0;
}

details pre code {
    background: transparent;
    padding: 0;
}