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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: #333;
    background: #fff;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Header & Navigation */
.header {
    background: #fff;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    position: sticky;
    top: 0;
    z-index: 1000;
}

.nav {
    padding: 1rem 0;
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

.nav-brand {
    display: flex;
    align-items: center;
    text-decoration: none;
    color: #333;
    font-weight: 600;
    font-size: 1.25rem;
}

.nav-logo {
    width: 40px;
    height: 40px;
    margin-right: 10px;
}

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

.nav-link {
    text-decoration: none;
    color: #666;
    font-weight: 500;
    transition: color 0.3s;
}

.nav-link:hover,
.nav-link.active {
    color: #6366f1;
}

.nav-toggle {
    display: none;
    flex-direction: column;
    background: none;
    border: none;
    cursor: pointer;
    padding: 5px;
}

.nav-toggle span {
    width: 25px;
    height: 3px;
    background: #333;
    margin: 3px 0;
    transition: 0.3s;
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 12px 24px;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 600;
    text-align: center;
    transition: all 0.3s;
    border: 2px solid transparent;
    cursor: pointer;
    font-size: 1rem;
}

.btn-primary {
    background: #6366f1;
    color: white;
    border-color: #6366f1;
}

.btn-primary:hover {
    background: #5855eb;
    border-color: #5855eb;
}

.btn-secondary {
    background: transparent;
    color: #6366f1;
    border-color: #6366f1;
}

.btn-secondary:hover {
    background: #6366f1;
    color: white;
}

.btn-outline {
    background: transparent;
    color: #333;
    border-color: #ddd;
}

.btn-outline:hover {
    background: #f8f9fa;
    border-color: #ccc;
}

.btn-success {
    background: #10b981;
    color: white;
    border-color: #10b981;
}

.btn-success:hover {
    background: #059669;
    border-color: #059669;
}

/* Hero Section */
.hero {
    background: linear-gradient(135deg, #f8fafc 0%, #e2e8f0 100%);
    padding: 80px 0;
    min-height: 600px;
    display: flex;
    align-items: center;
}

.hero .container {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
    align-items: center;
}

.hero-title {
    font-size: 3rem;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: 1.5rem;
    color: #1e293b;
}

.hero-description {
    font-size: 1.25rem;
    color: #64748b;
    margin-bottom: 2rem;
}

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

.hero-bg {
    width: 100%;
    height: auto;
    max-width: 500px;
}

/* Features Section */
.features {
    padding: 80px 0;
    background: #fff;
}

.section-title {
    text-align: center;
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 3rem;
    color: #1e293b;
}

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

.feature-card {
    text-align: center;
    padding: 2rem;
    border-radius: 12px;
    background: #f8fafc;
    transition: transform 0.3s;
}

.feature-card:hover {
    transform: translateY(-5px);
}

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

.feature-card h3 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 1rem;
    color: #1e293b;
}

.feature-card p {
    color: #64748b;
    line-height: 1.6;
}

/* Courses Section */
.featured-courses {
    padding: 80px 0;
    background: #f8fafc;
}

.courses-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: 2rem;
    margin-bottom: 3rem;
}

.course-card {
    background: white;
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    transition: transform 0.3s, box-shadow 0.3s;
}

.course-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
}

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

.course-content {
    padding: 1.5rem;
}

.course-category {
    display: inline-block;
    background: #e0e7ff;
    color: #6366f1;
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 0.875rem;
    font-weight: 500;
    margin-bottom: 1rem;
}

.course-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: #1e293b;
}

.course-description {
    color: #64748b;
    margin-bottom: 1rem;
    line-height: 1.6;
}

.course-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
    font-size: 0.875rem;
    color: #64748b;
}

.course-price {
    font-size: 1.5rem;
    font-weight: 700;
    color: #10b981;
    margin-bottom: 1rem;
}

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

/* Course Detail Page */
.course-detail {
    padding: 40px 0;
}

.course-header {
    background: #f8fafc;
    padding: 60px 0;
    margin-bottom: 40px;
}

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

.course-info h1 {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 1rem;
    color: #1e293b;
}

.course-info .course-meta {
    margin-bottom: 1.5rem;
}

.course-info .course-description {
    font-size: 1.125rem;
    margin-bottom: 2rem;
}

.course-sidebar {
    background: white;
    padding: 2rem;
    border-radius: 12px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    position: sticky;
    top: 100px;
}

.course-sidebar img {
    width: 100%;
    height: 200px;
    object-fit: cover;
    border-radius: 8px;
    margin-bottom: 1.5rem;
}

.course-tabs {
    display: flex;
    border-bottom: 2px solid #e2e8f0;
    margin-bottom: 2rem;
}

.tab-button {
    background: none;
    border: none;
    padding: 1rem 2rem;
    font-size: 1rem;
    font-weight: 500;
    color: #64748b;
    cursor: pointer;
    border-bottom: 2px solid transparent;
    transition: all 0.3s;
}

.tab-button.active {
    color: #6366f1;
    border-bottom-color: #6366f1;
}

.tab-content {
    display: none;
}

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

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

.curriculum-list li {
    padding: 1rem;
    border-bottom: 1px solid #e2e8f0;
    display: flex;
    align-items: center;
}

.curriculum-list li:before {
    content: "▶";
    color: #6366f1;
    margin-right: 1rem;
}

.instructor-section {
    display: flex;
    gap: 1rem;
    align-items: start;
}

.instructor-avatar {
    width: 80px;
    height: 80px;
    border-radius: 50%;
    background: #e2e8f0;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    font-weight: 600;
    color: #6366f1;
}

.faq-item {
    border: 1px solid #e2e8f0;
    border-radius: 8px;
    margin-bottom: 1rem;
    overflow: hidden;
}

.faq-question {
    width: 100%;
    background: #f8fafc;
    border: none;
    padding: 1rem;
    text-align: left;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.3s;
}

.faq-question:hover {
    background: #e2e8f0;
}

.faq-answer {
    padding: 1rem;
    display: none;
}

.faq-answer.active {
    display: block;
}

/* Checkout Pages */
.checkout {
    padding: 40px 0;
    background: #f8fafc;
    min-height: 80vh;
}

.checkout-container {
    max-width: 800px;
    margin: 0 auto;
}

.checkout-header {
    text-align: center;
    margin-bottom: 3rem;
}

.checkout-steps {
    display: flex;
    justify-content: center;
    margin-bottom: 3rem;
}

.step {
    display: flex;
    align-items: center;
    padding: 0.5rem 1rem;
    background: #e2e8f0;
    color: #64748b;
    border-radius: 20px;
    margin: 0 0.5rem;
}

.step.active {
    background: #6366f1;
    color: white;
}

.checkout-form {
    background: white;
    padding: 2rem;
    border-radius: 12px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

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

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: #374151;
}

.form-group input,
.form-group select,
.form-group textarea {
    width: 100%;
    padding: 12px;
    border: 2px solid #e5e7eb;
    border-radius: 8px;
    font-size: 1rem;
    transition: border-color 0.3s;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
    outline: none;
    border-color: #6366f1;
}

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

.error {
    color: #ef4444;
    font-size: 0.875rem;
    margin-top: 0.25rem;
}

.order-summary {
    background: #f8fafc;
    padding: 1.5rem;
    border-radius: 8px;
    margin-bottom: 2rem;
}

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

.payment-icon {
    width: 40px;
    height: 25px;
    background: #e2e8f0;
    border-radius: 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.75rem;
    font-weight: 600;
}

.security-badge {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: #10b981;
    font-size: 0.875rem;
    margin: 1rem 0;
}

.checkbox-group {
    display: flex;
    align-items: start;
    gap: 0.5rem;
    margin: 1.5rem 0;
}

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

/* Footer */
.footer {
    background: #1e293b;
    color: #e2e8f0;
    padding: 3rem 0 1rem;
}

.footer-content {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr;
    gap: 3rem;
    margin-bottom: 2rem;
}

.footer-section h3,
.footer-section h4 {
    margin-bottom: 1rem;
    color: white;
}

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

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

.footer-section a {
    color: #e2e8f0;
    text-decoration: none;
    transition: color 0.3s;
}

.footer-section a:hover {
    color: #6366f1;
}

.footer-contact p {
    margin-bottom: 0.5rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.footer-bottom {
    border-top: 1px solid #374151;
    padding-top: 1rem;
    text-align: center;
    color: #9ca3af;
}

/* Responsive Design */
@media (max-width: 768px) {
    .nav-menu {
        position: fixed;
        top: 70px;
        left: -100%;
        width: 100%;
        height: calc(100vh - 70px);
        background: white;
        flex-direction: column;
        justify-content: start;
        align-items: center;
        padding-top: 2rem;
        transition: left 0.3s;
        box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    }

    .nav-menu.active {
        left: 0;
    }

    .nav-toggle {
        display: flex;
    }

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

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

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

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

    .course-header .container {
        grid-template-columns: 1fr;
    }

    .course-sidebar {
        position: static;
    }

    .footer-content {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .form-row {
        grid-template-columns: 1fr;
    }

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

    .step {
        margin: 0.25rem 0;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 15px;
    }

    .hero {
        padding: 40px 0;
    }

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

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

    .features,
    .featured-courses {
        padding: 40px 0;
    }

    .course-card {
        margin: 0 10px;
    }
}

/* Form Validation Styles */
.form-group.error input,
.form-group.error select {
    border-color: #ef4444;
}

.form-group.success input,
.form-group.success select {
    border-color: #10b981;
}

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

/* Accessibility */
.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 States */
a:focus,
button:focus,
input:focus,
select:focus,
textarea:focus {
    outline: 2px solid #6366f1;
    outline-offset: 2px;
}