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

:root {
    /* Python Brand Colors */
    --python-blue: #3776ab;
    --python-yellow: #ffd343;
    --python-blue-dark: #2d5aa0;
    --python-yellow-dark: #f4c430;
    
    /* UI Colors */
    --primary: var(--python-blue);
    --primary-dark: var(--python-blue-dark);
    --secondary: var(--python-yellow);
    --secondary-dark: var(--python-yellow-dark);
    --success: #28a745;
    --warning: #ffc107;
    --error: #dc3545;
    --info: #17a2b8;
    
    /* Neutral Colors */
    --white: #ffffff;
    --gray-50: #f8f9fa;
    --gray-100: #e9ecef;
    --gray-200: #dee2e6;
    --gray-300: #ced4da;
    --gray-400: #adb5bd;
    --gray-500: #6c757d;
    --gray-600: #495057;
    --gray-700: #343a40;
    --gray-800: #212529;
    --gray-900: #0d1117;
    
    /* Typography */
    --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-family-mono: 'Fira Code', 'Monaco', 'Cascadia Code', 'Roboto Mono', monospace;
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    --spacing-3xl: 4rem;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    
    /* Border Radius */
    --radius-sm: 0.25rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    
    /* Transitions */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;
}

body {
    font-family: var(--font-family);
    line-height: 1.6;
    color: var(--gray-800);
    background-color: var(--gray-50);
    overflow-x: hidden;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* Navigation */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--gray-200);
    z-index: 1000;
    transition: var(--transition-normal);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 70px;
}

.nav-brand {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.nav-logo {
    width: 40px;
    height: 40px;
    object-fit: contain;
}

.nav-title {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--primary);
}

.nav-menu {
    display: flex;
    align-items: center;
    gap: var(--spacing-lg);
}

.nav-link {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-sm) var(--spacing-md);
    text-decoration: none;
    color: var(--gray-600);
    font-weight: 500;
    border-radius: var(--radius-md);
    transition: var(--transition-fast);
    position: relative;
}

.nav-link:hover {
    color: var(--primary);
    background-color: var(--gray-100);
}

.nav-link.active {
    color: var(--primary);
    background-color: rgba(55, 118, 171, 0.1);
}

.nav-toggle {
    display: none;
    flex-direction: column;
    cursor: pointer;
    gap: 4px;
}

.bar {
    width: 25px;
    height: 3px;
    background-color: var(--gray-600);
    border-radius: 2px;
    transition: var(--transition-fast);
}

/* Progress Bar */
.progress-container {
    position: fixed;
    top: 70px;
    left: 0;
    right: 0;
    height: 4px;
    background-color: var(--gray-200);
    z-index: 999;
}

.progress-bar {
    height: 100%;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    width: 0%;
    transition: width var(--transition-normal);
}

/* Main Content */
.main-content {
    margin-top: 74px;
    min-height: calc(100vh - 74px);
}

.section {
    display: none;
    min-height: calc(100vh - 74px);
    padding: var(--spacing-2xl) 0;
}

.section.active {
    display: block;
}

/* Hero Section */
.hero {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: var(--white);
    padding: var(--spacing-3xl) 0;
    margin-bottom: var(--spacing-3xl);
}

.hero-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-3xl);
    align-items: center;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-lg);
}

.highlight {
    color: var(--secondary);
    position: relative;
}

.highlight::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 3px;
    background-color: var(--secondary);
    border-radius: 2px;
}

.hero-description {
    font-size: 1.25rem;
    line-height: 1.6;
    margin-bottom: var(--spacing-xl);
    opacity: 0.9;
}

.hero-stats {
    display: flex;
    gap: var(--spacing-xl);
    margin-bottom: var(--spacing-xl);
}

.stat {
    text-align: center;
}

.stat-number {
    font-size: 2rem;
    font-weight: 700;
    color: var(--secondary);
}

.stat-label {
    font-size: 0.875rem;
    opacity: 0.8;
}

.hero-buttons {
    display: flex;
    gap: var(--spacing-md);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-md) var(--spacing-xl);
    border: none;
    border-radius: var(--radius-lg);
    font-size: 1rem;
    font-weight: 600;
    text-decoration: none;
    cursor: pointer;
    transition: var(--transition-fast);
    position: relative;
    overflow: hidden;
}

.btn-primary {
    background-color: var(--secondary);
    color: var(--gray-800);
}

.btn-primary:hover {
    background-color: var(--secondary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-secondary {
    background-color: transparent;
    color: var(--white);
    border: 2px solid var(--white);
}

.btn-secondary:hover {
    background-color: var(--white);
    color: var(--primary);
}

/* Code Preview */
.hero-visual {
    display: flex;
    justify-content: center;
    align-items: center;
}

.code-preview {
    background-color: var(--gray-900);
    border-radius: var(--radius-xl);
    overflow: hidden;
    box-shadow: var(--shadow-xl);
    width: 100%;
    max-width: 500px;
}

.code-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-md);
    background-color: var(--gray-800);
    border-bottom: 1px solid var(--gray-700);
}

.code-dots {
    display: flex;
    gap: var(--spacing-sm);
}

.dot {
    width: 12px;
    height: 12px;
    border-radius: 50%;
}

.dot.red { background-color: #ff5f56; }
.dot.yellow { background-color: #ffbd2e; }
.dot.green { background-color: #27ca3f; }

.code-title {
    color: var(--gray-300);
    font-size: 0.875rem;
    font-family: var(--font-family-mono);
}

.code-content {
    padding: var(--spacing-lg);
    font-family: var(--font-family-mono);
    font-size: 0.875rem;
    line-height: 1.6;
}

.code-line {
    display: flex;
    align-items: center;
    margin-bottom: var(--spacing-sm);
}

.line-number {
    color: var(--gray-500);
    margin-right: var(--spacing-md);
    min-width: 20px;
    text-align: right;
}

.code-text {
    color: var(--gray-100);
}

.keyword { color: #ff7b72; }
.string { color: #a5d6ff; }
.method { color: #d2a8ff; }
.variable { color: #79c0ff; }
.number { color: #79c0ff; }

.code-output {
    background-color: var(--gray-800);
    padding: var(--spacing-lg);
    border-top: 1px solid var(--gray-700);
}

.output-line {
    color: var(--secondary);
    font-family: var(--font-family-mono);
    font-size: 0.875rem;
    margin-bottom: var(--spacing-sm);
    opacity: 0;
}

/* Animations */
@keyframes typing {
    from { 
        opacity: 0;
        transform: translateX(-10px);
    }
    to { 
        opacity: 1;
        transform: translateX(0);
    }
}

.typing-animation {
    animation: typing 0.5s ease forwards;
}

/* Features Section */
.features {
    padding: var(--spacing-3xl) 0;
}

.section-title {
    text-align: center;
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--gray-800);
    margin-bottom: var(--spacing-3xl);
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-xl);
}

.feature-card {
    background-color: var(--white);
    padding: var(--spacing-xl);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-md);
    text-align: center;
    transition: var(--transition-normal);
    border: 1px solid var(--gray-200);
}

.feature-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-xl);
    border-color: var(--primary);
}

.feature-icon {
    width: 80px;
    height: 80px;
    background: linear-gradient(135deg, var(--primary), var(--primary-dark));
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto var(--spacing-lg);
    color: var(--white);
    font-size: 2rem;
}

.feature-card h3 {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--gray-800);
    margin-bottom: var(--spacing-md);
}

.feature-card p {
    color: var(--gray-600);
    line-height: 1.6;
}

/* Footer */
.footer {
    background-color: var(--gray-800);
    color: var(--gray-300);
    padding: var(--spacing-3xl) 0 var(--spacing-xl);
    margin-top: var(--spacing-3xl);
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-xl);
    margin-bottom: var(--spacing-xl);
}

.footer-section h3 {
    color: var(--white);
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
}

.creator-name {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--secondary);
    margin-bottom: var(--spacing-xs);
}

.creator-title {
    color: var(--gray-400);
    font-style: italic;
}

.footer-section ul {
    list-style: none;
}

.footer-section ul li {
    margin-bottom: var(--spacing-sm);
}

.footer-section ul li a {
    color: var(--gray-400);
    text-decoration: none;
    transition: var(--transition-fast);
}

.footer-section ul li a:hover {
    color: var(--secondary);
}

.social-links {
    display: flex;
    gap: var(--spacing-md);
}

.social-link {
    width: 40px;
    height: 40px;
    background-color: var(--gray-700);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--gray-400);
    text-decoration: none;
    transition: var(--transition-fast);
}

.social-link:hover {
    background-color: var(--primary);
    color: var(--white);
    transform: translateY(-2px);
}

.footer-bottom {
    text-align: center;
    padding-top: var(--spacing-xl);
    border-top: 1px solid var(--gray-700);
    color: var(--gray-500);
}

/* Loading Screen */
.loading-screen {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--white);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
    transition: opacity var(--transition-slow), visibility var(--transition-slow);
}

.loading-screen.hidden {
    opacity: 0;
    visibility: hidden;
}

.loading-content {
    text-align: center;
}

.loading-logo img {
    width: 80px;
    height: 80px;
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.1); }
}

.loading-text {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--primary);
    margin: var(--spacing-lg) 0;
}

.loading-bar {
    width: 300px;
    height: 4px;
    background-color: var(--gray-200);
    border-radius: 2px;
    overflow: hidden;
}

.loading-progress {
    height: 100%;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    width: 0%;
    animation: loading 3s ease-in-out infinite;
}

@keyframes loading {
    0% { width: 0%; }
    50% { width: 70%; }
    100% { width: 100%; }
}

/* Responsive Design */
@media (max-width: 768px) {
    .nav-menu {
        position: fixed;
        top: 70px;
        left: -100%;
        width: 100%;
        height: calc(100vh - 70px);
        background-color: var(--white);
        flex-direction: column;
        justify-content: flex-start;
        align-items: center;
        padding-top: var(--spacing-xl);
        transition: var(--transition-normal);
        box-shadow: var(--shadow-lg);
    }
    
    .nav-menu.active {
        left: 0;
    }
    
    .nav-toggle {
        display: flex;
    }
    
    .nav-toggle.active .bar:nth-child(1) {
        transform: rotate(45deg) translate(5px, 5px);
    }
    
    .nav-toggle.active .bar:nth-child(2) {
        opacity: 0;
    }
    
    .nav-toggle.active .bar:nth-child(3) {
        transform: rotate(-45deg) translate(7px, -6px);
    }
    
    .hero-content {
        grid-template-columns: 1fr;
        text-align: center;
        gap: var(--spacing-xl);
    }
    
    .hero-title {
        font-size: 2.5rem;
    }
    
    .hero-stats {
        justify-content: center;
    }
    
    .hero-buttons {
        justify-content: center;
        flex-wrap: wrap;
    }
    
    .features-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-content {
        grid-template-columns: 1fr;
        text-align: center;
    }
}

@media (max-width: 480px) {
    .hero-title {
        font-size: 2rem;
    }
    
    .hero-stats {
        flex-direction: column;
        gap: var(--spacing-md);
    }
    
    .hero-buttons {
        flex-direction: column;
        align-items: center;
    }
    
    .btn {
        width: 100%;
        max-width: 300px;
        justify-content: center;
    }
}


/* Additional styles for content sections */

/* Section Layout */
.section-header {
    text-align: center;
    margin-bottom: var(--spacing-3xl);
}

.section-description {
    font-size: 1.25rem;
    color: var(--gray-600);
    max-width: 800px;
    margin: 0 auto var(--spacing-xl);
    line-height: 1.6;
}

.content-grid {
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: var(--spacing-3xl);
    align-items: start;
}

.content-main {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xl);
}

.content-sidebar {
    position: sticky;
    top: 100px;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

/* Topic Cards */
.topic-card {
    background: var(--white);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-md);
    overflow: hidden;
    transition: var(--transition-normal);
    border: 1px solid var(--gray-200);
}

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

.topic-header {
    background: linear-gradient(135deg, var(--primary), var(--primary-dark));
    color: var(--white);
    padding: var(--spacing-lg);
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.topic-header h2 {
    font-size: 1.5rem;
    font-weight: 600;
    margin: 0;
}

.topic-icon {
    font-size: 1.5rem;
    opacity: 0.8;
}

.topic-content {
    padding: var(--spacing-xl);
}

.topic-content > p {
    font-size: 1.1rem;
    color: var(--gray-600);
    margin-bottom: var(--spacing-lg);
    line-height: 1.6;
}

/* Code Examples */
.code-example {
    background: var(--gray-900);
    border-radius: var(--radius-lg);
    overflow: hidden;
    margin: var(--spacing-lg) 0;
    box-shadow: var(--shadow-lg);
}

.code-header {
    background: var(--gray-800);
    padding: var(--spacing-md) var(--spacing-lg);
    display: flex;
    align-items: center;
    justify-content: space-between;
    border-bottom: 1px solid var(--gray-700);
}

.code-title {
    color: var(--gray-300);
    font-size: 0.875rem;
    font-weight: 500;
}

.run-code-btn {
    background: var(--secondary);
    color: var(--gray-800);
    border: none;
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    transition: var(--transition-fast);
}

.run-code-btn:hover {
    background: var(--secondary-dark);
    transform: translateY(-1px);
}

.code-block {
    background: var(--gray-900);
    color: var(--gray-100);
    padding: var(--spacing-lg);
    font-family: var(--font-family-mono);
    font-size: 0.875rem;
    line-height: 1.6;
    overflow-x: auto;
    margin: 0;
}

.code-output {
    background: var(--gray-800);
    border-top: 1px solid var(--gray-700);
    min-height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.code-execution-loading {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    color: var(--gray-400);
    font-size: 0.875rem;
}

.code-execution-result {
    width: 100%;
}

.execution-header {
    background: var(--gray-700);
    padding: var(--spacing-sm) var(--spacing-lg);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    color: var(--gray-300);
    font-size: 0.875rem;
    font-weight: 500;
}

.execution-output {
    background: var(--gray-800);
    color: var(--secondary);
    padding: var(--spacing-lg);
    font-family: var(--font-family-mono);
    font-size: 0.875rem;
    line-height: 1.6;
    margin: 0;
    white-space: pre-wrap;
}

/* Interactive Questions */
.interactive-question {
    background: rgba(55, 118, 171, 0.05);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    margin: var(--spacing-lg) 0;
    border-left: 4px solid var(--primary);
}

.question-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: var(--spacing-md);
}

.question-header h3 {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--gray-800);
    margin: 0;
}

.question-difficulty {
    background: var(--secondary);
    color: var(--gray-800);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
}

.question-text {
    font-size: 1.1rem;
    color: var(--gray-700);
    margin-bottom: var(--spacing-lg);
    line-height: 1.6;
}

.question-options {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.option-btn {
    background: var(--white);
    border: 2px solid var(--gray-300);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition-fast);
    text-align: center;
}

.option-btn:hover:not(:disabled) {
    border-color: var(--primary);
    background: rgba(55, 118, 171, 0.05);
}

.option-btn:disabled {
    cursor: not-allowed;
    opacity: 0.7;
}

.option-btn.selected {
    border-color: var(--primary);
    background: rgba(55, 118, 171, 0.1);
}

.question-feedback {
    background: var(--white);
    border-radius: var(--radius-md);
    padding: var(--spacing-lg);
    margin-top: var(--spacing-md);
    box-shadow: var(--shadow-sm);
}

.question-feedback.correct {
    border-left: 4px solid var(--success);
}

.question-feedback.incorrect {
    border-left: 4px solid var(--error);
}

.feedback-content {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.feedback-text {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-weight: 600;
    margin: 0;
}

.feedback-text i {
    font-size: 1.25rem;
}

.feedback-explanation {
    color: var(--gray-600);
    line-height: 1.6;
}

/* Visual Demonstrations */
.visual-demo {
    background: var(--white);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    margin: var(--spacing-lg) 0;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--gray-200);
}

.string-visual {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-md);
}

.string-chars {
    display: flex;
    gap: 2px;
}

.char-box {
    width: 50px;
    height: 50px;
    background: var(--primary);
    color: var(--white);
    display: flex;
    align-items: center;
    justify-content: center;
    font-family: var(--font-family-mono);
    font-size: 1.25rem;
    font-weight: 600;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: var(--transition-fast);
    position: relative;
}

.char-box:hover {
    transform: scale(1.1);
    box-shadow: var(--shadow-md);
}

.index-labels {
    display: flex;
    gap: 2px;
    font-family: var(--font-family-mono);
    font-size: 0.875rem;
    font-weight: 600;
}

.index-labels.positive {
    color: var(--primary);
}

.index-labels.negative {
    color: var(--error);
}

.index-labels span {
    width: 50px;
    text-align: center;
    padding: var(--spacing-xs);
}

.character-info {
    background: var(--gray-50);
    border-radius: var(--radius-md);
    padding: var(--spacing-lg);
    margin-top: var(--spacing-lg);
    opacity: 0;
    transform: translateY(10px);
    transition: var(--transition-normal);
}

.character-info.show {
    opacity: 1;
    transform: translateY(0);
}

.char-info-content h4 {
    color: var(--gray-800);
    margin-bottom: var(--spacing-md);
    font-size: 1.1rem;
}

.char-details {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: var(--spacing-sm);
}

.char-detail {
    display: flex;
    justify-content: space-between;
    padding: var(--spacing-sm);
    background: var(--white);
    border-radius: var(--radius-sm);
}

.char-detail .label {
    font-weight: 500;
    color: var(--gray-600);
}

.char-detail .value {
    font-family: var(--font-family-mono);
    font-weight: 600;
    color: var(--primary);
}

/* Progress Cards */
.progress-card {
    background: var(--white);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
    border: 1px solid var(--gray-200);
}

.progress-card h3 {
    color: var(--gray-800);
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-lg);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.progress-item {
    margin-bottom: var(--spacing-md);
}

.progress-item span {
    display: block;
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--gray-600);
    margin-bottom: var(--spacing-xs);
}

.progress-bar-small {
    width: 100%;
    height: 8px;
    background: var(--gray-200);
    border-radius: 4px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    border-radius: 4px;
    transition: width var(--transition-slow);
}

.progress-item.completed {
    opacity: 0.8;
}

.progress-item.completed span {
    color: var(--success);
}

.progress-item.completed .progress-fill {
    background: var(--success);
}

/* Tips Cards */
.tips-card {
    background: linear-gradient(135deg, var(--secondary), var(--secondary-dark));
    color: var(--gray-800);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-md);
}

.tips-card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-lg);
}

.tips-card ul {
    list-style: none;
    margin: 0;
    padding: 0;
}

.tips-card li {
    position: relative;
    padding-left: var(--spacing-lg);
    margin-bottom: var(--spacing-sm);
    line-height: 1.6;
}

.tips-card li::before {
    content: '💡';
    position: absolute;
    left: 0;
    top: 0;
}

/* Loading Placeholders */
.loading-placeholder {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-3xl);
    color: var(--gray-500);
    text-align: center;
}

.loading-placeholder i {
    font-size: 3rem;
    margin-bottom: var(--spacing-lg);
    color: var(--primary);
}

.loading-placeholder p {
    font-size: 1.1rem;
    margin: 0;
}

/* About Section Styles */
.about-content {
    max-width: 1000px;
    margin: 0 auto;
}

.about-hero {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--spacing-3xl);
    align-items: center;
    margin-bottom: var(--spacing-3xl);
}

.about-text h1 {
    margin-bottom: var(--spacing-lg);
}

.about-description {
    font-size: 1.25rem;
    color: var(--gray-600);
    line-height: 1.6;
}

.about-image {
    width: 100%;
    height: 300px;
    object-fit: cover;
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-lg);
}

.creator-section {
    margin-bottom: var(--spacing-3xl);
}

.creator-card {
    background: linear-gradient(135deg, var(--primary), var(--primary-dark));
    color: var(--white);
    border-radius: var(--radius-xl);
    padding: var(--spacing-3xl);
    text-align: center;
    box-shadow: var(--shadow-xl);
}

.creator-info h2 {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: var(--spacing-sm);
    color: var(--secondary);
}

.creator-title {
    font-size: 1.25rem;
    margin-bottom: var(--spacing-lg);
    opacity: 0.9;
}

.creator-bio {
    font-size: 1.1rem;
    line-height: 1.6;
    margin-bottom: var(--spacing-xl);
    opacity: 0.9;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

.creator-stats {
    display: flex;
    justify-content: center;
    gap: var(--spacing-3xl);
}

.course-features h2 {
    text-align: center;
    font-size: 2rem;
    font-weight: 700;
    color: var(--gray-800);
    margin-bottom: var(--spacing-xl);
}

.feature-item {
    text-align: center;
    padding: var(--spacing-xl);
}

.feature-item i {
    font-size: 3rem;
    color: var(--primary);
    margin-bottom: var(--spacing-lg);
}

.feature-item h3 {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--gray-800);
    margin-bottom: var(--spacing-md);
}

.feature-item p {
    color: var(--gray-600);
    line-height: 1.6;
}

/* Notifications */
.notification {
    position: fixed;
    top: 100px;
    right: var(--spacing-lg);
    background: var(--white);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-xl);
    border-left: 4px solid var(--info);
    z-index: 1000;
    min-width: 300px;
    animation: slideInRight 0.3s ease-out;
}

.notification-info {
    border-left-color: var(--info);
}

.notification-success {
    border-left-color: var(--success);
}

.notification-warning {
    border-left-color: var(--warning);
}

.notification-error {
    border-left-color: var(--error);
}

.notification-content {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--spacing-lg);
}

.notification-message {
    font-weight: 500;
    color: var(--gray-700);
}

.notification-close {
    background: none;
    border: none;
    font-size: 1.25rem;
    color: var(--gray-500);
    cursor: pointer;
    padding: 0;
    margin-left: var(--spacing-md);
}

.notification-close:hover {
    color: var(--gray-700);
}

/* Responsive Design for Content */
@media (max-width: 1024px) {
    .content-grid {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
    }
    
    .content-sidebar {
        position: static;
        order: -1;
    }
    
    .about-hero {
        grid-template-columns: 1fr;
        text-align: center;
    }
    
    .creator-stats {
        flex-direction: column;
        gap: var(--spacing-lg);
    }
}

@media (max-width: 768px) {
    .question-options {
        grid-template-columns: 1fr;
    }
    
    .string-chars {
        flex-wrap: wrap;
        justify-content: center;
    }
    
    .char-details {
        grid-template-columns: 1fr;
    }
    
    .index-labels {
        flex-wrap: wrap;
        justify-content: center;
    }
    
    .creator-card {
        padding: var(--spacing-xl);
    }
    
    .creator-info h2 {
        font-size: 1.5rem;
    }
}

@media (max-width: 480px) {
    .topic-content {
        padding: var(--spacing-lg);
    }
    
    .code-block {
        font-size: 0.75rem;
        padding: var(--spacing-md);
    }
    
    .char-box {
        width: 40px;
        height: 40px;
        font-size: 1rem;
    }
    
    .index-labels span {
        width: 40px;
    }
    
    .notification {
        right: var(--spacing-sm);
        left: var(--spacing-sm);
        min-width: auto;
    }
}