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

:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary-color: #64748b;
    --accent-color: #f59e0b;
    --success-color: #10b981;
    --error-color: #ef4444;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-light: #94a3b8;
    --bg-primary: #ffffff;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #f1f5f9;
    --border-color: #e2e8f0;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-mono: 'SF Mono', Monaco, 'Cascadia Code', monospace;
}

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

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
}

/* Header */
.header {
    background: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 1rem 1rem;
}

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

.logo-link {
    display: flex;
    align-items: center;
    text-decoration: none;
    color: var(--text-primary);
}

.logo {
    width: 32px;
    height: 32px;
    margin-right: 0.5rem;
}

.brand-name {
    font-size: 1.25rem;
    font-weight: 700;
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: 2rem;
}

.nav-link {
    text-decoration: none;
    color: var(--text-secondary);
    font-weight: 500;
    transition: color 0.2s;
}

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

.nav-toggle {
    display: none;
    flex-direction: column;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
}

.nav-toggle span {
    width: 20px;
    height: 2px;
    background: var(--text-primary);
    margin: 2px 0;
    transition: 0.3s;
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-md);
    text-decoration: none;
    font-weight: 600;
    text-align: center;
    cursor: pointer;
    border: none;
    transition: all 0.2s;
    font-size: 0.875rem;
}

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

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

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

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

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

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

.btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}

/* Hero Section */
.hero {
    padding: 4rem 0;
    background: linear-gradient(135deg, var(--bg-secondary) 0%, var(--bg-tertiary) 100%);
}

.hero .container {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 3rem;
    align-items: center;
}

.hero-title {
    font-size: 3rem;
    font-weight: 800;
    line-height: 1.1;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.hero-subtitle {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-bottom: 2rem;
    line-height: 1.6;
}

.hero-actions {
    display: flex;
    gap: 1rem;
}

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

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

/* Sections */
.section-title {
    font-size: 2.5rem;
    font-weight: 700;
    text-align: center;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.section-subtitle {
    font-size: 1.125rem;
    color: var(--text-secondary);
    text-align: center;
    margin-bottom: 3rem;
}

.section-actions {
    text-align: center;
    margin-top: 3rem;
}

/* Features */
.features {
    padding: 5rem 0;
}

.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
}

.feature-card {
    background: var(--bg-primary);
    padding: 2rem;
    border-radius: var(--radius-lg);
    text-align: center;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border-color);
}

.feature-icon {
    font-size: 3rem;
    margin-bottom: 1rem;
}

.feature-card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

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

/* Featured Courses */
.featured-courses {
    padding: 5rem 0;
    background: var(--bg-secondary);
}

.courses-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.course-card {
    background: var(--bg-primary);
    border-radius: var(--radius-lg);
    overflow: hidden;
    box-shadow: var(--shadow-md);
    transition: transform 0.2s, box-shadow 0.2s;
    border: 1px solid var(--border-color);
}

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

.course-image {
    width: 100%;
    height: 200px;
    object-fit: cover;
}

.course-content {
    padding: 1.5rem;
}

.course-category {
    display: inline-block;
    background: var(--bg-tertiary);
    color: var(--primary-color);
    font-size: 0.75rem;
    font-weight: 600;
    padding: 0.25rem 0.75rem;
    border-radius: var(--radius-sm);
    margin-bottom: 0.75rem;
    text-transform: uppercase;
}

.course-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.course-title a {
    text-decoration: none;
    color: inherit;
}

.course-title a:hover {
    color: var(--primary-color);
}

.course-description {
    color: var(--text-secondary);
    margin-bottom: 1rem;
    line-height: 1.5;
    font-size: 0.875rem;
}

.course-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
    font-size: 0.875rem;
    color: var(--text-light);
}

.course-price {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 1rem;
}

/* Forms */
.form-group {
    margin-bottom: 1.5rem;
}

.form-label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--text-primary);
}

.form-input,
.form-select,
.form-textarea {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: 1rem;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.form-input:focus,
.form-select:focus,
.form-textarea:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

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

.form-error {
    color: var(--error-color);
    font-size: 0.875rem;
    margin-top: 0.25rem;
}

.form-checkbox {
    display: flex;
    align-items: flex-start;
    gap: 0.75rem;
}

.form-checkbox input {
    margin-top: 0.25rem;
}

/* Course Filters */
.course-filters {
    background: var(--bg-primary);
    padding: 2rem 0;
    border-bottom: 1px solid var(--border-color);
}

.filters-row {
    display: grid;
    grid-template-columns: 1fr auto auto;
    gap: 1rem;
    align-items: center;
}

.search-box {
    position: relative;
}

.search-input {
    padding-left: 2.5rem;
}

.search-icon {
    position: absolute;
    left: 0.75rem;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-light);
}

/* Course Detail */
.course-header {
    padding: 3rem 0;
    background: var(--bg-secondary);
}

.course-header-content {
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: 3rem;
    align-items: start;
}

.course-badge {
    display: inline-block;
    background: var(--accent-color);
    color: white;
    padding: 0.5rem 1rem;
    border-radius: var(--radius-sm);
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

.course-detail-title {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.course-detail-meta {
    display: flex;
    gap: 2rem;
    margin-bottom: 1.5rem;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.course-purchase-card {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 2rem;
    position: sticky;
    top: 2rem;
}

.course-detail-price {
    font-size: 2rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 1.5rem;
}

.course-includes {
    margin-bottom: 2rem;
}

.course-includes h4 {
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.course-includes ul {
    list-style: none;
    space-y: 0.5rem;
}

.course-includes li {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-secondary);
    font-size: 0.875rem;
}

.course-includes li::before {
    content: '✓';
    color: var(--success-color);
    font-weight: bold;
}

/* Checkout */
.checkout-header {
    background: var(--bg-secondary);
    padding: 2rem 0;
    border-bottom: 1px solid var(--border-color);
}

.checkout-steps {
    display: flex;
    justify-content: center;
    gap: 2rem;
    margin-bottom: 2rem;
}

.checkout-step {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    border-radius: var(--radius-md);
    font-weight: 600;
    color: var(--text-light);
}

.checkout-step.active {
    background: var(--primary-color);
    color: white;
}

.checkout-step.completed {
    background: var(--success-color);
    color: white;
}

.checkout-content {
    padding: 3rem 0;
}

.checkout-grid {
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: 3rem;
}

.order-summary {
    background: var(--bg-secondary);
    padding: 2rem;
    border-radius: var(--radius-lg);
    border: 1px solid var(--border-color);
}

.order-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 0;
    border-bottom: 1px solid var(--border-color);
}

.order-total {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 0;
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
}

.payment-icons {
    display: flex;
    gap: 0.5rem;
    align-items: center;
    margin: 1rem 0;
}

.payment-icon {
    width: 40px;
    height: 24px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.75rem;
    font-weight: bold;
    color: var(--text-secondary);
}

/* Footer */
.footer {
    background: var(--text-primary);
    color: white;
    padding: 3rem 0 1rem;
    margin-top: 4rem;
}

.footer-content {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr 1.5fr;
    gap: 2rem;
    margin-bottom: 2rem;
}

.footer-brand {
    display: flex;
    align-items: center;
    margin-bottom: 1rem;
}

.footer-logo {
    width: 32px;
    height: 32px;
    margin-right: 0.5rem;
    filter: brightness(0) invert(1);
}

.footer-brand-name {
    font-size: 1.25rem;
    font-weight: 700;
}

.footer-description {
    color: #94a3b8;
    line-height: 1.6;
}

.footer-title {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

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

.footer-links li {
    margin-bottom: 0.5rem;
}

.footer-links a {
    color: #94a3b8;
    text-decoration: none;
    transition: color 0.2s;
}

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

.footer-contact p {
    color: #94a3b8;
    margin-bottom: 0.5rem;
}

.footer-contact a {
    color: #94a3b8;
    text-decoration: none;
}

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

.footer-bottom {
    border-top: 1px solid #374151;
    padding-top: 1rem;
    text-align: center;
    color: #94a3b8;
}

/* Responsive Design */
@media (max-width: 768px) {
    .nav-menu {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--bg-primary);
        flex-direction: column;
        padding: 1rem;
        box-shadow: var(--shadow-md);
        gap: 0.5rem;
    }

    .nav-menu.active {
        display: flex;
    }

    .nav-toggle {
        display: flex;
    }

    .hero .container {
        grid-template-columns: 1fr;
        gap: 2rem;
        text-align: center;
    }

    .hero-title {
        font-size: 2rem;
    }

    .hero-actions {
        justify-content: center;
        flex-wrap: wrap;
    }

    .section-title {
        font-size: 2rem;
    }

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

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

    .course-header-content {
        grid-template-columns: 1fr;
        gap: 2rem;
    }

    .course-detail-title {
        font-size: 1.75rem;
    }

    .course-detail-meta {
        flex-wrap: wrap;
        gap: 1rem;
    }

    .checkout-grid {
        grid-template-columns: 1fr;
        gap: 2rem;
    }

    .checkout-steps {
        flex-direction: column;
        align-items: center;
        gap: 1rem;
    }

    .filters-row {
        grid-template-columns: 1fr;
        gap: 1rem;
    }

    .footer-content {
        grid-template-columns: 1fr;
        gap: 2rem;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 0.75rem;
    }

    .hero {
        padding: 2rem 0;
    }

    .hero-title {
        font-size: 1.75rem;
    }

    .hero-subtitle {
        font-size: 1rem;
    }

    .section-title {
        font-size: 1.75rem;
    }

    .btn {
        padding: 0.625rem 1.25rem;
        font-size: 0.875rem;
    }

    .course-card {
        margin: 0 -0.75rem;
        border-radius: 0;
    }

    .feature-card {
        padding: 1.5rem;
    }
}

/* 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 */
a:focus,
button:focus,
input:focus,
select:focus,
textarea:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* Loading states */
.loading {
    opacity: 0.6;
    pointer-events: none;
}

.spinner {
    border: 2px solid #f3f3f3;
    border-top: 2px solid var(--primary-color);
    border-radius: 50%;
    width: 20px;
    height: 20px;
    animation: spin 1s linear infinite;
    display: inline-block;
    margin-right: 0.5rem;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}