/* === Base Styles === */
:root {
    --primary: #667eea;
    --primary-dark: #5a6fd6;
    --secondary: #764ba2;
    --success: #10b981;
    --warning: #f59e0b;
    --danger: #ef4444;
    --info: #3b82f6;
    
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --bg-card: #1e293b;
    
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --text-muted: #64748b;
    
    --border: #334155;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4);
    
    --radius: 12px;
    --radius-sm: 8px;
    --radius-lg: 16px;
    
    --sidebar-width: 280px;
    --header-height: 70px;
    
    --transition: all 0.2s ease;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

a {
    color: var(--primary);
    text-decoration: none;
    transition: var(--transition);
}

a:hover {
    color: var(--primary-dark);
}

/* === Buttons === */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 12px 24px;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 14px;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    color: white;
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(102, 126, 234, 0.4);
}

.btn-outline {
    background: transparent;
    border: 1px solid var(--border);
    color: var(--text-primary);
}

.btn-outline:hover {
    background: var(--bg-tertiary);
}

.btn-block {
    width: 100%;
}

/* === Forms === */
.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    font-size: 14px;
    font-weight: 500;
    color: var(--text-secondary);
}

.form-group input,
.form-group textarea,
.form-group select {
    width: 100%;
    padding: 14px 16px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 15px;
    color: var(--text-primary);
    transition: var(--transition);
}

.form-group input:focus,
.form-group textarea:focus,
.form-group select:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.2);
}

.form-group input::placeholder,
.form-group textarea::placeholder {
    color: var(--text-muted);
}

.form-error {
    padding: 12px 16px;
    background: rgba(239, 68, 68, 0.1);
    border: 1px solid rgba(239, 68, 68, 0.3);
    border-radius: var(--radius-sm);
    color: var(--danger);
    font-size: 14px;
    margin-bottom: 20px;
}

.password-input {
    position: relative;
}

.password-input input {
    padding-right: 50px;
}

.toggle-password {
    position: absolute;
    right: 12px;
    top: 50%;
    transform: translateY(-50%);
    background: none;
    border: none;
    color: var(--text-muted);
    cursor: pointer;
    padding: 4px;
}

/* === Login Page === */
.login-page {
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    padding: 20px;
}

.login-container {
    position: relative;
    width: 100%;
    max-width: 420px;
}

.login-box {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 40px;
    position: relative;
    z-index: 1;
}

.login-header {
    text-align: center;
    margin-bottom: 32px;
}

.login-header .logo {
    margin-bottom: 20px;
}

.login-header h1 {
    font-size: 24px;
    font-weight: 600;
    margin-bottom: 8px;
}

.login-header p {
    color: var(--text-secondary);
    font-size: 14px;
}

.login-footer {
    text-align: center;
    margin-top: 24px;
    font-size: 13px;
    color: var(--text-muted);
}

.login-bg {
    position: fixed;
    inset: 0;
    overflow: hidden;
    pointer-events: none;
}

.bg-shape {
    position: absolute;
    border-radius: 50%;
    filter: blur(100px);
    opacity: 0.3;
}

.bg-shape-1 {
    width: 400px;
    height: 400px;
    background: var(--primary);
    top: -100px;
    right: -100px;
}

.bg-shape-2 {
    width: 300px;
    height: 300px;
    background: var(--secondary);
    bottom: -50px;
    left: -50px;
}

.bg-shape-3 {
    width: 200px;
    height: 200px;
    background: var(--info);
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

/* === Loading === */
.loading {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 60px 20px;
    color: var(--text-secondary);
}

.loading-spinner {
    width: 40px;
    height: 40px;
    border: 3px solid var(--border);
    border-top-color: var(--primary);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
    margin-bottom: 16px;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

.spinner {
    animation: spin 0.8s linear infinite;
}

/* === App Layout === */
.app {
    display: flex;
    min-height: 100vh;
}

/* === Sidebar === */
.sidebar {
    width: var(--sidebar-width);
    background: var(--bg-secondary);
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    z-index: 100;
    transition: transform 0.3s ease;
}

.sidebar-header {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 20px;
    border-bottom: 1px solid var(--border);
}

.sidebar-header .back-link {
    color: var(--text-secondary);
}

.sidebar-header .back-link:hover {
    color: var(--text-primary);
}

.logo-text {
    font-size: 18px;
    font-weight: 600;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.sidebar-nav {
    flex: 1;
    padding: 16px;
    overflow-y: auto;
}

.nav-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 16px;
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    transition: var(--transition);
    margin-bottom: 4px;
    cursor: pointer;
    background: none;
    border: none;
    width: 100%;
    text-align: left;
    font-size: 14px;
}

.nav-item:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

.nav-item.active {
    background: rgba(102, 126, 234, 0.15);
    color: var(--primary);
}

.nav-item svg {
    flex-shrink: 0;
}

.sidebar-footer {
    padding: 16px;
    border-top: 1px solid var(--border);
}

.nav-item.logout:hover {
    color: var(--danger);
}

/* === Modules Nav === */
.modules-nav {
    flex: 1;
    padding: 16px;
    overflow-y: auto;
}

.module-group {
    margin-bottom: 24px;
}

.module-title {
    font-size: 12px;
    font-weight: 600;
    text-transform: uppercase;
    color: var(--text-muted);
    padding: 0 12px;
    margin-bottom: 8px;
    letter-spacing: 0.5px;
}

.lesson-link {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 10px 12px;
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    font-size: 14px;
    transition: var(--transition);
    cursor: pointer;
}

.lesson-link:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

.lesson-link.active {
    background: rgba(102, 126, 234, 0.15);
    color: var(--primary);
}

.lesson-link.completed {
    color: var(--success);
}

.lesson-link .status-icon {
    width: 18px;
    height: 18px;
    border-radius: 50%;
    border: 2px solid currentColor;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}

.lesson-link.completed .status-icon {
    background: var(--success);
    border-color: var(--success);
}

.lesson-link.completed .status-icon svg {
    width: 10px;
    height: 10px;
    stroke: white;
}

/* === Main Content === */
.main-content {
    flex: 1;
    margin-left: var(--sidebar-width);
    display: flex;
    flex-direction: column;
}

.main-header {
    height: var(--header-height);
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 24px;
    position: sticky;
    top: 0;
    z-index: 50;
}

.header-left {
    display: flex;
    align-items: center;
    gap: 16px;
}

.page-title {
    font-size: 20px;
    font-weight: 600;
}

.mobile-menu-btn {
    display: none;
    background: none;
    border: none;
    color: var(--text-primary);
    cursor: pointer;
    padding: 8px;
}

.header-right {
    display: flex;
    align-items: center;
    gap: 16px;
}

.user-info {
    display: flex;
    align-items: center;
    gap: 12px;
}

.user-name {
    font-size: 14px;
    color: var(--text-secondary);
}

.user-avatar {
    width: 36px;
    height: 36px;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    font-size: 14px;
}

.content {
    flex: 1;
    padding: 24px;
}

/* === Empty State === */
.empty-state {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    padding: 80px 20px;
    color: var(--text-secondary);
}

.empty-state svg {
    margin-bottom: 24px;
    opacity: 0.5;
}

.empty-state h2 {
    font-size: 20px;
    font-weight: 600;
    margin-bottom: 8px;
    color: var(--text-primary);
}

/* === Courses Grid === */
.courses-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 24px;
}

.course-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    overflow: hidden;
    transition: var(--transition);
}

.course-card:hover {
    transform: translateY(-4px);
    border-color: var(--primary);
    box-shadow: var(--shadow-lg);
}

.course-cover {
    width: 100%;
    height: 160px;
    object-fit: cover;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
}

.course-body {
    padding: 20px;
}

.course-title {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 8px;
}

.course-meta {
    display: flex;
    gap: 16px;
    color: var(--text-muted);
    font-size: 13px;
    margin-bottom: 16px;
}

.course-meta span {
    display: flex;
    align-items: center;
    gap: 6px;
}

.course-progress {
    margin-bottom: 16px;
}

.progress-bar {
    height: 6px;
    background: var(--bg-tertiary);
    border-radius: 3px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    border-radius: 3px;
    transition: width 0.5s ease;
}

.progress-text {
    font-size: 12px;
    color: var(--text-muted);
    margin-top: 6px;
}

/* === Select Lesson === */
.select-lesson {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    text-align: center;
    padding: 80px 20px;
    color: var(--text-secondary);
}

.select-lesson svg {
    margin-bottom: 24px;
    opacity: 0.3;
}

.select-lesson h2 {
    font-size: 20px;
    font-weight: 600;
    margin-bottom: 8px;
    color: var(--text-primary);
}

/* === Lesson Content === */
.lesson-content {
    max-width: 800px;
    margin: 0 auto;
}

.lesson-blocks {
    padding: 20px 0;
}

/* Block styles */
.block {
    margin-bottom: 24px;
}

.block-text p {
    font-size: 16px;
    line-height: 1.8;
    color: var(--text-secondary);
}

.block-heading h1 {
    font-size: 28px;
    font-weight: 700;
    margin-bottom: 16px;
}

.block-heading h2 {
    font-size: 22px;
    font-weight: 600;
    margin-bottom: 12px;
}

.block-heading h3 {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 8px;
}

.block-image {
    border-radius: var(--radius);
    overflow: hidden;
}

.block-image img {
    width: 100%;
    display: block;
}

.block-image figcaption {
    padding: 12px;
    text-align: center;
    font-size: 14px;
    color: var(--text-muted);
    background: var(--bg-secondary);
}

.block-video {
    border-radius: var(--radius);
    overflow: hidden;
}

.block-video video {
    width: 100%;
    display: block;
}

.block-code {
    background: var(--bg-secondary);
    border-radius: var(--radius);
    overflow: hidden;
}

.block-code pre {
    padding: 20px;
    overflow-x: auto;
    font-family: 'Fira Code', 'Monaco', monospace;
    font-size: 14px;
    line-height: 1.5;
}

.block-quote {
    border-left: 4px solid var(--primary);
    padding: 16px 24px;
    background: var(--bg-secondary);
    border-radius: 0 var(--radius) var(--radius) 0;
}

.block-quote blockquote {
    font-size: 16px;
    font-style: italic;
    color: var(--text-secondary);
}

.block-quote cite {
    display: block;
    margin-top: 8px;
    font-size: 14px;
    color: var(--text-muted);
}

.block-list ul,
.block-list ol {
    padding-left: 24px;
    color: var(--text-secondary);
}

.block-list li {
    margin-bottom: 8px;
}

.block-divider hr {
    border: none;
    height: 1px;
    background: var(--border);
    margin: 32px 0;
}

.block-callout {
    display: flex;
    gap: 12px;
    padding: 16px 20px;
    border-radius: var(--radius);
    background: rgba(102, 126, 234, 0.1);
    border: 1px solid rgba(102, 126, 234, 0.2);
}

.block-callout.warning {
    background: rgba(245, 158, 11, 0.1);
    border-color: rgba(245, 158, 11, 0.2);
}

.block-callout.error {
    background: rgba(239, 68, 68, 0.1);
    border-color: rgba(239, 68, 68, 0.2);
}

.block-callout .emoji {
    font-size: 20px;
}

/* === Homework Section === */
.homework-section {
    margin-top: 40px;
    padding-top: 40px;
    border-top: 1px solid var(--border);
}

.homework-section h2 {
    font-size: 20px;
    margin-bottom: 16px;
}

.homework-content {
    padding: 20px;
    background: var(--bg-secondary);
    border-radius: var(--radius);
    margin-bottom: 24px;
}

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

/* === Responsive === */
@media (max-width: 768px) {
    .sidebar {
        transform: translateX(-100%);
    }
    
    .sidebar.open {
        transform: translateX(0);
    }
    
    .main-content {
        margin-left: 0;
    }
    
    .mobile-menu-btn {
        display: block;
    }
    
    .courses-grid {
        grid-template-columns: 1fr;
    }
    
    .header-right .user-name {
        display: none;
    }
}