/* Modern Learning Platform - CSS */
:root {
    --primary-color: #4f46e5; /* Indigo 600 */
    --primary-hover: #4338ca; /* Indigo 700 */
    --secondary-color: #0ea5e9; /* Sky 500 */
    --accent-color: #f59e0b; /* Amber 500 */
    --dark-text: #1e293b; /* Slate 800 */
    --light-text: #64748b; /* Slate 500 */
    --bg-light: #f8fafc; /* Slate 50 */
    --bg-white: #ffffff;
    --border-color: #e2e8f0; /* Slate 200 */
    --gradient-hero: linear-gradient(135deg, #4f46e5 0%, #0ea5e9 100%);
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --font-main: 'Inter', sans-serif;
    --container-width: 1200px;
}

/* Reset & Base */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: var(--font-main);
    color: var(--dark-text);
    background-color: var(--bg-light);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

a {
    text-decoration: none;
    color: inherit;
    transition: color 0.2s ease;
}

ul {
    list-style: none;
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

/* Utilities */
.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 0 1.5rem;
}

.section {
    padding: 4rem 0;
}

.text-center { text-align: center; }
.text-primary { color: var(--primary-color); }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-4 { margin-bottom: 2rem; }

.btn {
    display: inline-block;
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-md);
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    border: none;
    font-size: 1rem;
}

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

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

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

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

/* Header & Nav */
.site-header {
    background-color: var(--bg-white);
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 100;
}

.navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 80px;
}

.logo {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--primary-color);
    letter-spacing: -0.5px;
}

.nav-links {
    display: flex;
    gap: 2rem;
}

.nav-links a {
    font-weight: 500;
    color: var(--light-text);
}

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

.mobile-menu-btn {
    display: none;
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--dark-text);
}

/* Modal Popup */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.3s ease, visibility 0.3s ease;
}

.modal-overlay.active {
    opacity: 1;
    visibility: visible;
}

.modal-content {
    background-color: white;
    padding: 2.5rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    text-align: center;
    max-width: 400px;
    width: 90%;
    transform: translateY(20px);
    transition: transform 0.3s ease;
}

.modal-overlay.active .modal-content {
    transform: translateY(0);
}

.modal-icon {
    width: 60px;
    height: 60px;
    background-color: #d1fae5; /* Green 100 */
    color: #059669; /* Green 600 */
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    margin: 0 auto 1.5rem;
}

.modal-title {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
    color: var(--dark-text);
}

.modal-message {
    color: var(--light-text);
    margin-bottom: 2rem;
}

.modal-close {
    width: 100%;
    padding: 0.75rem;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: var(--radius-md);
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.2s ease;
}

.modal-close:hover {
    background-color: var(--primary-hover);
}

/* Newsletter Section */
.newsletter-section {
    background-color: #f1f5f9; /* Slate 100 */
    padding: 5rem 0;
    text-align: center;
}

.newsletter-form {
    max-width: 500px;
    margin: 2rem auto 0;
    display: flex;
    gap: 0.5rem;
}

@media (max-width: 640px) {
    .newsletter-form {
        flex-direction: column;
    }
}

.newsletter-input {
    flex-grow: 1;
    padding: 0.75rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: 1rem;
    font-family: inherit;
}

.newsletter-input:focus {
    outline: 2px solid var(--primary-color);
    border-color: transparent;
}

/* Footer */
.site-footer {
    background-color: #111827; /* Gray 900 */
    color: #9ca3af; /* Gray 400 */
    padding: 4rem 0 2rem;
    margin-top: auto;
}

.footer-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 3rem;
    margin-bottom: 3rem;
}

.footer-col h3 {
    color: white;
    margin-bottom: 1.5rem;
    font-size: 1.1rem;
}

.footer-links li {
    margin-bottom: 0.75rem;
}

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

.footer-bottom {
    border-top: 1px solid #374151; /* Gray 700 */
    padding-top: 2rem;
    text-align: center;
    font-size: 0.875rem;
}

/* Responsive */
@media (max-width: 768px) {
    .nav-links {
        display: none; /* Hidden by default on mobile, toggled via JS */
        position: absolute;
        top: 80px;
        left: 0;
        right: 0;
        background-color: var(--bg-white);
        flex-direction: column;
        padding: 1rem;
        box-shadow: var(--shadow-md);
        text-align: center;
    }

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

    .mobile-menu-btn {
        display: block;
    }
}