/* ==========================================================================
   Docker DevOps Learning Platform Design System
   Color Palette: Docker Blue, Electric Cyan, Deep Carbon Canvas, Glass Surface
   ========================================================================== */

:root {
    --bg-main: #0b0f19;
    --bg-card: #111827;
    --bg-card-hover: #1b2438;
    --bg-sidebar: #0e1322;
    --bg-header: #0d1220;
    
    --docker-blue: #2496ed;
    --docker-cyan: #0db7ed;
    --docker-navy: #091e42;
    --accent-glow: rgba(36, 150, 237, 0.3);

    --text-primary: #f3f4f6;
    --text-secondary: #9ca3af;
    --text-muted: #6b7280;
    --border-color: rgba(36, 150, 237, 0.18);
    --border-color-hover: rgba(36, 150, 237, 0.4);

    --success-color: #10b981;
    --warning-color: #f59e0b;
    --danger-color: #ef4444;
    --info-color: #3b82f6;

    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-mono: 'JetBrains Mono', monospace;

    --radius-sm: 6px;
    --radius-md: 10px;
    --radius-lg: 16px;
    --shadow-soft: 0 4px 20px rgba(0, 0, 0, 0.4);
    --shadow-glow: 0 0 15px rgba(36, 150, 237, 0.25);
}

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

body {
    font-family: var(--font-sans);
    background-color: var(--bg-main);
    color: var(--text-primary);
    line-height: 1.6;
    overflow-x: hidden;
}

/* Header Navbar */
.app-header {
    height: 70px;
    background: var(--bg-header);
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 24px;
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(12px);
}

.brand {
    display: flex;
    align-items: center;
    gap: 14px;
}

.brand-icon {
    width: 42px;
    height: 42px;
    background: linear-gradient(135deg, var(--docker-blue), var(--docker-cyan));
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: var(--shadow-glow);
}

.brand-icon svg {
    width: 26px;
    height: 26px;
    color: #ffffff;
}

.brand-text h1 {
    font-size: 1.15rem;
    font-weight: 800;
    background: linear-gradient(90deg, #ffffff, var(--docker-cyan));
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
    letter-spacing: -0.3px;
}

.brand-text span {
    font-size: 0.75rem;
    color: var(--text-secondary);
    display: block;
}

/* Header Center Search */
.header-center {
    flex: 1;
    max-width: 480px;
    margin: 0 20px;
}

.search-box {
    position: relative;
    width: 100%;
}

.search-box input {
    width: 100%;
    background: rgba(17, 24, 39, 0.8);
    border: 1px solid var(--border-color);
    border-radius: 20px;
    padding: 8px 16px 8px 40px;
    color: var(--text-primary);
    font-size: 0.88rem;
    transition: all 0.25s ease;
}

.search-box input:focus {
    outline: none;
    border-color: var(--docker-blue);
    box-shadow: 0 0 10px rgba(36, 150, 237, 0.3);
}

.search-icon {
    position: absolute;
    left: 14px;
    top: 50%;
    transform: translateY(-50%);
    font-size: 0.85rem;
    color: var(--text-muted);
}

/* Progress Widget */
.header-actions {
    display: flex;
    align-items: center;
    gap: 16px;
}

.progress-widget {
    display: flex;
    align-items: center;
    gap: 10px;
    background: rgba(17, 24, 39, 0.6);
    padding: 6px 14px;
    border-radius: 20px;
    border: 1px solid var(--border-color);
}

.progress-bar-bg {
    width: 110px;
    height: 8px;
    background: #1f2937;
    border-radius: 4px;
    overflow: hidden;
}

.progress-bar-fill {
    height: 100%;
    width: 0%;
    background: linear-gradient(90deg, var(--docker-blue), var(--docker-cyan));
    transition: width 0.4s ease;
}

.progress-text {
    font-size: 0.78rem;
    font-weight: 600;
    color: var(--docker-cyan);
}

/* App Container Layout */
.app-container {
    display: flex;
    min-height: calc(100vh - 70px);
}

/* Sidebar Navigation */
.app-sidebar {
    width: 340px;
    background: var(--bg-sidebar);
    border-right: 1px solid var(--border-color);
    padding: 20px 16px;
    display: flex;
    flex-direction: column;
    gap: 16px;
    overflow-y: auto;
    height: calc(100vh - 70px);
    position: sticky;
    top: 70px;
}

.sidebar-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-weight: 700;
    font-size: 0.95rem;
    color: var(--text-primary);
    padding-bottom: 8px;
    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

/* Category Filter Pills */
.category-filter-container {
    display: flex;
    gap: 6px;
    flex-wrap: wrap;
}

.category-pill {
    background: rgba(31, 41, 55, 0.8);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    padding: 4px 10px;
    border-radius: 12px;
    font-size: 0.73rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
}

.category-pill:hover,
.category-pill.active {
    background: var(--docker-blue);
    color: #ffffff;
    border-color: var(--docker-blue);
    box-shadow: 0 0 8px rgba(36, 150, 237, 0.4);
}

.sidebar-exam-btn {
    width: 100%;
    background: linear-gradient(135deg, #1e3a8a, #0284c7);
    color: #ffffff;
    border: 1px solid var(--docker-cyan);
    padding: 10px 14px;
    border-radius: var(--radius-md);
    font-weight: 700;
    font-size: 0.85rem;
    cursor: pointer;
    transition: all 0.25s ease;
    text-align: center;
    box-shadow: 0 4px 12px rgba(2, 132, 199, 0.3);
}

.sidebar-exam-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 18px rgba(2, 132, 199, 0.5);
}

/* Chapter Items List */
#chapterListContainer {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.chapter-item {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 12px 14px;
    cursor: pointer;
    transition: all 0.2s ease;
    position: relative;
}

.chapter-item:hover {
    background: var(--bg-card-hover);
    border-color: var(--border-color-hover);
    transform: translateX(3px);
}

.chapter-item.active {
    background: linear-gradient(135deg, rgba(36, 150, 237, 0.15), rgba(13, 183, 237, 0.08));
    border-color: var(--docker-blue);
    box-shadow: inset 3px 0 0 var(--docker-blue);
}

.chapter-item-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 4px;
}

.chapter-item-num {
    font-size: 0.72rem;
    font-weight: 700;
    color: var(--docker-cyan);
}

.chapter-item-title {
    font-size: 0.88rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 4px;
    line-height: 1.3;
}

.chapter-item-footer {
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-size: 0.72rem;
    color: var(--text-muted);
}

/* Status Badges */
.badge {
    display: inline-block;
    padding: 2px 8px;
    border-radius: 10px;
    font-size: 0.7rem;
    font-weight: 700;
    text-transform: uppercase;
}

.badge-blue { background: rgba(36, 150, 237, 0.2); color: var(--docker-cyan); border: 1px solid rgba(36, 150, 237, 0.4); }
.badge-green { background: rgba(16, 185, 129, 0.2); color: var(--success-color); border: 1px solid rgba(16, 185, 129, 0.4); }
.badge-purple { background: rgba(168, 85, 247, 0.2); color: #c084fc; border: 1px solid rgba(168, 85, 247, 0.4); }
.badge-orange { background: rgba(245, 158, 11, 0.2); color: var(--warning-color); border: 1px solid rgba(245, 158, 11, 0.4); }

/* Main Content Section */
.main-content {
    flex: 1;
    padding: 24px 32px;
    display: flex;
    flex-direction: column;
    gap: 20px;
    max-width: 1200px;
}

/* Chapter Header Banner */
.chapter-header {
    background: linear-gradient(135deg, rgba(17, 24, 39, 0.9), rgba(9, 30, 66, 0.95));
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 24px 28px;
    box-shadow: var(--shadow-soft);
    position: relative;
    overflow: hidden;
}

.chapter-header::before {
    content: '';
    position: absolute;
    top: -50px;
    right: -50px;
    width: 200px;
    height: 200px;
    background: radial-gradient(circle, rgba(36, 150, 237, 0.15), transparent 70%);
    pointer-events: none;
}

.chapter-meta {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 10px;
}

.video-timestamp {
    font-size: 0.78rem;
    color: var(--text-secondary);
    background: rgba(0, 0, 0, 0.3);
    padding: 3px 10px;
    border-radius: 12px;
}

.chapter-header h2 {
    font-size: 1.6rem;
    font-weight: 800;
    color: #ffffff;
    margin-bottom: 8px;
    letter-spacing: -0.4px;
}

.chapter-desc {
    font-size: 0.92rem;
    color: var(--text-secondary);
    margin-bottom: 18px;
    max-width: 900px;
}

.chapter-actions {
    display: flex;
    gap: 12px;
}

/* Buttons */
.btn {
    padding: 8px 18px;
    border-radius: var(--radius-md);
    font-weight: 600;
    font-size: 0.85rem;
    cursor: pointer;
    transition: all 0.2s ease;
    border: none;
    display: inline-flex;
    align-items: center;
    gap: 8px;
}

.btn-primary {
    background: linear-gradient(135deg, var(--docker-blue), #0284c7);
    color: #ffffff;
    box-shadow: 0 4px 12px rgba(36, 150, 237, 0.3);
}

.btn-primary:hover {
    background: linear-gradient(135deg, #1d4ed8, #0369a1);
    box-shadow: 0 6px 16px rgba(36, 150, 237, 0.5);
}

.btn-secondary {
    background: rgba(31, 41, 55, 0.9);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

.btn-secondary:hover {
    background: rgba(55, 65, 81, 0.9);
    border-color: var(--border-color-hover);
}

/* Navigation Tabs */
.tabs-nav {
    display: flex;
    gap: 10px;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 2px;
}

.tab-btn {
    background: transparent;
    border: none;
    color: var(--text-secondary);
    padding: 10px 18px;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    border-bottom: 3px solid transparent;
    transition: all 0.2s ease;
}

.tab-btn:hover {
    color: var(--text-primary);
}

.tab-btn.active {
    color: var(--docker-cyan);
    border-bottom-color: var(--docker-cyan);
}

/* Tab Panels */
.tab-panel {
    display: none;
    animation: fadeIn 0.3s ease-in-out;
}

.tab-panel.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(6px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Article Content Styles */
.article-content {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 30px 36px;
    box-shadow: var(--shadow-soft);
}

.article-content h2 {
    font-size: 1.4rem;
    color: var(--docker-cyan);
    margin: 24px 0 12px 0;
    padding-bottom: 6px;
    border-bottom: 1px solid rgba(36, 150, 237, 0.15);
}

.article-content h3 {
    font-size: 1.15rem;
    color: #ffffff;
    margin: 20px 0 10px 0;
}

.article-content p {
    margin-bottom: 14px;
    color: #d1d5db;
    font-size: 0.95rem;
}

.article-content ul, .article-content ol {
    margin: 0 0 16px 24px;
    color: #d1d5db;
}

.article-content li {
    margin-bottom: 6px;
}

/* Callout Alerts */
.alert {
    padding: 16px 20px;
    border-radius: var(--radius-md);
    margin: 18px 0;
    font-size: 0.9rem;
}

.alert-info { background: rgba(59, 130, 246, 0.12); border-left: 4px solid var(--docker-blue); color: #93c5fd; }
.alert-tip { background: rgba(16, 185, 129, 0.12); border-left: 4px solid var(--success-color); color: #a7f3d0; }
.alert-warning { background: rgba(245, 158, 11, 0.12); border-left: 4px solid var(--warning-color); color: #fde68a; }

/* Code Blocks */
pre {
    background: #090d16;
    border: 1px solid rgba(255, 255, 255, 0.1);
    border-radius: var(--radius-md);
    padding: 16px 20px;
    overflow-x: auto;
    margin: 16px 0;
}

code {
    font-family: var(--font-mono);
    font-size: 0.88rem;
    color: #38bdf8;
}

p code, li code {
    background: rgba(36, 150, 237, 0.15);
    padding: 2px 6px;
    border-radius: 4px;
    color: #7dd3fc;
}

/* Video Player */
.video-player-container {
    width: 100%;
    aspect-ratio: 16 / 9;
    background: #000000;
    border-radius: var(--radius-lg);
    overflow: hidden;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-soft);
}

.video-player-container iframe {
    width: 100%;
    height: 100%;
    border: none;
}

.video-meta-box {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 20px;
    margin-top: 16px;
}

/* Playground / Terminal */
.playground-container {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.playground-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 20px 24px;
    box-shadow: var(--shadow-soft);
}

.playground-title {
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-weight: 700;
    font-size: 0.95rem;
    color: #ffffff;
    margin-bottom: 12px;
}

.chip-btn {
    background: rgba(36, 150, 237, 0.12);
    border: 1px solid rgba(36, 150, 237, 0.3);
    color: var(--docker-cyan);
    padding: 4px 10px;
    border-radius: 12px;
    font-size: 0.75rem;
    font-family: var(--font-mono);
    cursor: pointer;
    transition: all 0.2s ease;
}

.chip-btn:hover {
    background: var(--docker-blue);
    color: #ffffff;
}

.editor-textarea {
    width: 100%;
    height: 120px;
    background: #090d16;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 14px;
    color: #38bdf8;
    font-family: var(--font-mono);
    font-size: 0.9rem;
    resize: vertical;
}

.editor-textarea:focus {
    outline: none;
    border-color: var(--docker-blue);
}

.terminal-output {
    background: #05080f;
    border: 1px solid rgba(255, 255, 255, 0.08);
    border-radius: var(--radius-md);
    padding: 16px 20px;
    min-height: 180px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    color: #a7f3d0;
    white-space: pre-wrap;
    line-height: 1.5;
}

/* Quiz Container */
.quiz-container {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 28px 32px;
}

.quiz-question-title {
    font-size: 1.1rem;
    font-weight: 700;
    color: #ffffff;
    margin-bottom: 16px;
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-bottom: 20px;
}

.quiz-option {
    background: rgba(31, 41, 55, 0.7);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 12px 16px;
    cursor: pointer;
    font-size: 0.9rem;
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    gap: 12px;
}

.quiz-option:hover {
    background: var(--bg-card-hover);
    border-color: var(--docker-blue);
}

.quiz-option.selected {
    border-color: var(--docker-blue);
    background: rgba(36, 150, 237, 0.15);
}

.quiz-option.correct {
    background: rgba(16, 185, 129, 0.2);
    border-color: var(--success-color);
    color: #a7f3d0;
}

.quiz-option.wrong {
    background: rgba(239, 68, 68, 0.2);
    border-color: var(--danger-color);
    color: #fca5a5;
}

.quiz-feedback {
    margin-top: 16px;
    padding: 14px;
    border-radius: var(--radius-md);
    font-size: 0.88rem;
}

/* Notes Container */
.notes-container {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 28px 32px;
}

.notes-textarea {
    width: 100%;
    height: 250px;
    background: #090d16;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 16px;
    color: var(--text-primary);
    font-family: var(--font-sans);
    font-size: 0.92rem;
    resize: vertical;
    margin-bottom: 16px;
}

/* Footer Navigation */
.footer-nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-top: 24px;
    padding-top: 16px;
    border-top: 1px solid var(--border-color);
}

/* Modal Overlay */
.modal-overlay {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background: rgba(0, 0, 0, 0.8);
    backdrop-filter: blur(8px);
    z-index: 1000;
    align-items: center;
    justify-content: center;
}

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

.modal-content {
    background: var(--bg-card);
    border: 1px solid var(--docker-blue);
    border-radius: var(--radius-lg);
    width: 90%;
    max-width: 800px;
    max-height: 85vh;
    overflow-y: auto;
    padding: 32px;
    position: relative;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.7);
}

.modal-close {
    position: absolute;
    top: 20px;
    right: 20px;
    background: rgba(255, 255, 255, 0.1);
    border: none;
    color: #ffffff;
    width: 32px;
    height: 32px;
    border-radius: 50%;
    cursor: pointer;
}