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

:root {
    --primary-color: hsl(240, 100%, 60%);
    --primary-hover: hsl(240, 100%, 55%);
    --secondary-color: hsl(210, 15%, 25%);
    --accent-color: hsl(45, 100%, 60%);
    --text-primary: hsl(210, 15%, 20%);
    --text-secondary: hsl(210, 10%, 40%);
    --text-light: hsl(210, 5%, 60%);
    --background: hsl(0, 0%, 100%);
    --background-light: hsl(210, 20%, 98%);
    --background-section: hsl(210, 25%, 96%);
    --border-color: hsl(210, 15%, 90%);
    --border-light: hsl(210, 10%, 95%);
    --shadow: 0 2px 10px hsla(210, 15%, 20%, 0.1);
    --shadow-hover: 0 4px 20px hsla(210, 15%, 20%, 0.15);
    --border-radius: 8px;
    --transition: all 0.3s ease;
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 1.875rem;
    --font-size-4xl: 2.25rem;
    --font-size-5xl: 3rem;
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    --spacing-3xl: 4rem;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--background);
}

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

/* Header */
.header {
    background: var(--background);
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 100;
}

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

.nav-brand {
    display: flex;
    align-items: center;
}

.brand-link {
    display: flex;
    align-items: center;
    text-decoration: none;
    color: var(--text-primary);
    font-weight: 700;
    font-size: var(--font-size-xl);
}

.brand-logo {
    width: 40px;
    height: 40px;
    margin-right: var(--spacing-sm);
}

.brand-text {
    display: none;
}

.nav-menu {
    display: none;
    list-style: none;
    align-items: center;
    gap: var(--spacing-lg);
}

.nav-link {
    text-decoration: none;
    color: var(--text-secondary);
    font-weight: 500;
    transition: var(--transition);
    padding: var(--spacing-sm) 0;
    position: relative;
}

.nav-link:hover,
.nav-link.active {
    color: var(--primary-color);
}

.nav-link.active::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: var(--primary-color);
}

.nav-toggle {
    display: flex;
    flex-direction: column;
    background: none;
    border: none;
    cursor: pointer;
    padding: var(--spacing-sm);
    gap: 4px;
}

.nav-toggle span {
    width: 25px;
    height: 3px;
    background: var(--text-primary);
    transition: var(--transition);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-sm) var(--spacing-lg);
    border: 2px solid transparent;
    border-radius: var(--border-radius);
    text-decoration: none;
    font-weight: 600;
    font-size: var(--font-size-base);
    cursor: pointer;
    transition: var(--transition);
    min-height: 44px;
}

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

.btn-primary:hover {
    background: var(--primary-hover);
    border-color: var(--primary-hover);
    transform: translateY(-1px);
}

.btn-secondary {
    background: transparent;
    color: var(--text-primary);
    border-color: var(--border-color);
}

.btn-secondary:hover {
    background: var(--background-light);
    border-color: var(--text-primary);
}

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

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

/* Hero Section */
.hero {
    padding: var(--spacing-3xl) 0;
    background: linear-gradient(135deg, var(--background-light) 0%, var(--background-section) 100%);
}

.hero .container {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-2xl);
    align-items: center;
}

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

.hero-title {
    font-size: var(--font-size-4xl);
    font-weight: 800;
    margin-bottom: var(--spacing-lg);
    line-height: 1.2;
}

.hero-description {
    font-size: var(--font-size-lg);
    color: var(--text-secondary);
    margin-bottom: var(--spacing-2xl);
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

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

.hero-image {
    display: flex;
    justify-content: center;
}

.hero-bg {
    max-width: 100%;
    height: auto;
}

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

.section-title {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    text-align: center;
    margin-bottom: var(--spacing-2xl);
}

.features-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-xl);
}

.feature-card {
    text-align: center;
    padding: var(--spacing-xl);
    border-radius: var(--border-radius);
    background: var(--background-light);
}

.feature-icon {
    font-size: var(--font-size-4xl);
    margin-bottom: var(--spacing-lg);
}

.feature-card h3 {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin-bottom: var(--spacing-md);
}

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

/* Featured Courses */
.featured-courses {
    padding: var(--spacing-3xl) 0;
    background: var(--background-section);
}

.courses-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-xl);
    margin-bottom: var(--spacing-2xl);
}

.course-card {
    background: var(--background);
    border-radius: var(--border-radius);
    overflow: hidden;
    box-shadow: var(--shadow);
    transition: var(--transition);
}

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

.course-image {
    position: relative;
    height: 200px;
    overflow: hidden;
}

.course-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.course-label {
    position: absolute;
    top: var(--spacing-md);
    right: var(--spacing-md);
    background: var(--accent-color);
    color: var(--text-primary);
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--border-radius);
    font-size: var(--font-size-sm);
    font-weight: 600;
}

.course-content {
    padding: var(--spacing-lg);
}

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

.course-category {
    background: var(--primary-color);
    color: white;
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--border-radius);
    font-size: var(--font-size-sm);
    font-weight: 500;
}

.course-difficulty {
    color: var(--text-light);
    font-size: var(--font-size-sm);
}

.course-title {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin-bottom: var(--spacing-md);
}

.course-description {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-lg);
    line-height: 1.5;
}

.course-details {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-lg);
    padding-top: var(--spacing-md);
    border-top: 1px solid var(--border-light);
}

.course-duration {
    color: var(--text-light);
    font-size: var(--font-size-sm);
}

.course-price {
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--primary-color);
}

.section-actions {
    text-align: center;
}

/* Search and Filter */
.search-filter {
    padding: var(--spacing-2xl) 0;
    background: var(--background-light);
}

.filter-controls {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-xl);
}

.search-box {
    position: relative;
}

.search-input {
    width: 100%;
    padding: var(--spacing-md);
    border: 2px solid var(--border-color);
    border-radius: var(--border-radius);
    font-size: var(--font-size-base);
    transition: var(--transition);
}

.search-input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.category-filters {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-sm);
}

.filter-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    border: 2px solid var(--border-color);
    border-radius: var(--border-radius);
    background: var(--background);
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
    cursor: pointer;
    transition: var(--transition);
}

.filter-btn:hover,
.filter-btn.active {
    border-color: var(--primary-color);
    color: var(--primary-color);
}

/* Course Detail */
.course-detail {
    padding: var(--spacing-2xl) 0;
}

.course-header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
}

.course-hero-title {
    font-size: var(--font-size-4xl);
    font-weight: 700;
    margin-bottom: var(--spacing-md);
}

.course-hero-meta {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-lg);
}

.course-info-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-2xl);
}

.course-main {
    background: var(--background);
    padding: var(--spacing-xl);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

.course-sidebar {
    background: var(--background-light);
    padding: var(--spacing-xl);
    border-radius: var(--border-radius);
    border: 1px solid var(--border-light);
}

.section-heading {
    font-size: var(--font-size-2xl);
    font-weight: 600;
    margin-bottom: var(--spacing-lg);
    padding-bottom: var(--spacing-md);
    border-bottom: 2px solid var(--border-light);
}

.list-styled {
    list-style: none;
    padding: 0;
}

.list-styled li {
    padding: var(--spacing-sm) 0;
    position: relative;
    padding-left: var(--spacing-lg);
}

.list-styled li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--primary-color);
    font-weight: 600;
}

.curriculum-list {
    list-style: none;
    padding: 0;
}

.curriculum-item {
    padding: var(--spacing-md);
    border: 1px solid var(--border-light);
    border-radius: var(--border-radius);
    margin-bottom: var(--spacing-sm);
    background: var(--background-light);
}

.curriculum-title {
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
}

.curriculum-desc {
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
}

.instructor-card {
    background: var(--background);
    padding: var(--spacing-lg);
    border-radius: var(--border-radius);
    border: 1px solid var(--border-light);
    margin-bottom: var(--spacing-lg);
}

.instructor-name {
    font-size: var(--font-size-lg);
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
}

.instructor-bio {
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
    line-height: 1.5;
}

.faq-list {
    list-style: none;
    padding: 0;
}

.faq-item {
    margin-bottom: var(--spacing-lg);
}

.faq-question {
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.faq-answer {
    color: var(--text-secondary);
    line-height: 1.5;
}

/* Forms */
.form-group {
    margin-bottom: var(--spacing-lg);
}

.form-label {
    display: block;
    margin-bottom: var(--spacing-sm);
    font-weight: 500;
    color: var(--text-primary);
}

.form-input,
.form-textarea {
    width: 100%;
    padding: var(--spacing-md);
    border: 2px solid var(--border-color);
    border-radius: var(--border-radius);
    font-size: var(--font-size-base);
    font-family: inherit;
    transition: var(--transition);
}

.form-input:focus,
.form-textarea:focus {
    outline: none;
    border-color: var(--primary-color);
}

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

/* Content Pages */
.content-page {
    padding: var(--spacing-2xl) 0;
}

.content-header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
}

.page-title {
    font-size: var(--font-size-4xl);
    font-weight: 700;
    margin-bottom: var(--spacing-md);
}

.page-description {
    font-size: var(--font-size-lg);
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto;
}

.content-section {
    background: var(--background);
    padding: var(--spacing-xl);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    margin-bottom: var(--spacing-xl);
}

.content-section h2 {
    font-size: var(--font-size-2xl);
    font-weight: 600;
    margin-bottom: var(--spacing-lg);
    color: var(--text-primary);
}

.content-section h3 {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin: var(--spacing-lg) 0 var(--spacing-md) 0;
    color: var(--text-primary);
}

.content-section p {
    margin-bottom: var(--spacing-md);
    line-height: 1.6;
    color: var(--text-secondary);
}

.content-section ul,
.content-section ol {
    margin-bottom: var(--spacing-md);
    padding-left: var(--spacing-xl);
}

.content-section li {
    margin-bottom: var(--spacing-sm);
    color: var(--text-secondary);
}

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

.footer-content {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-xl);
    margin-bottom: var(--spacing-xl);
}

.footer-section h3,
.footer-section h4 {
    margin-bottom: var(--spacing-lg);
    font-weight: 600;
}

.footer-brand p {
    color: rgba(255, 255, 255, 0.8);
    margin-top: var(--spacing-md);
}

.footer-logo {
    width: 32px;
    height: 32px;
    margin-bottom: var(--spacing-md);
    filter: brightness(0) invert(1);
}

.footer-links {
    list-style: none;
    padding: 0;
}

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

.footer-links a {
    color: rgba(255, 255, 255, 0.8);
    text-decoration: none;
    transition: var(--transition);
}

.footer-links a:hover {
    color: white;
}

.contact-info p {
    margin-bottom: var(--spacing-sm);
    color: rgba(255, 255, 255, 0.8);
}

.contact-info a {
    color: rgba(255, 255, 255, 0.8);
    text-decoration: none;
    transition: var(--transition);
}

.contact-info a:hover {
    color: white;
}

.footer-bottom {
    text-align: center;
    padding-top: var(--spacing-xl);
    border-top: 1px solid rgba(255, 255, 255, 0.2);
    color: rgba(255, 255, 255, 0.6);
}

/* Responsive Design */
@media (min-width: 640px) {
    .brand-text {
        display: block;
    }
    
    .hero-actions {
        flex-direction: row;
        justify-content: center;
    }
    
    .features-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .courses-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .filter-controls {
        flex-direction: row;
        align-items: center;
    }
    
    .search-box {
        flex: 1;
        max-width: 400px;
    }
}

@media (min-width: 768px) {
    .nav-menu {
        display: flex;
    }
    
    .nav-toggle {
        display: none;
    }
    
    .hero .container {
        grid-template-columns: 1fr 1fr;
        text-align: left;
    }
    
    .hero-content {
        text-align: left;
    }
    
    .hero-description {
        margin-left: 0;
        margin-right: 0;
    }
    
    .hero-actions {
        justify-content: flex-start;
    }
    
    .course-info-grid {
        grid-template-columns: 2fr 1fr;
    }
    
    .footer-content {
        grid-template-columns: 2fr 1fr 1fr 1fr;
    }
}

@media (min-width: 1024px) {
    .features-grid {
        grid-template-columns: repeat(4, 1fr);
    }
    
    .courses-grid {
        grid-template-columns: repeat(3, 1fr);
    }
}

/* Mobile Navigation */
@media (max-width: 767px) {
    .nav-menu {
        position: fixed;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--background);
        flex-direction: column;
        padding: var(--spacing-lg);
        box-shadow: var(--shadow);
        transform: translateY(-100%);
        opacity: 0;
        visibility: hidden;
        transition: var(--transition);
    }
    
    .nav-menu.active {
        transform: translateY(0);
        opacity: 1;
        visibility: visible;
    }
    
    .nav-link {
        padding: var(--spacing-md) 0;
        border-bottom: 1px solid var(--border-light);
    }
    
    .nav-link:last-child {
        border-bottom: none;
    }
}

/* Accessibility */
@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* Focus styles */
.btn:focus,
.nav-link:focus,
.form-input:focus,
.form-textarea:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}