/* Base Styles */
:root {
    --primary-color: #1a237e;
    --secondary-color: #7986cb;
    --accent-color: #ff4081;
    --text-color: #333;
    --light-text: #fff;
    --background-color: #f5f5f5;
    --card-background: #fff;
    --header-gradient-start: #1a237e;
    --header-gradient-end: #3949ab;
    --section-border: #e0e0e0;
}

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

body {
    font-family: 'Roboto', Arial, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--background-color);
}

.container {
    width: 90%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 15px;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
    margin-bottom: 1rem;
    line-height: 1.2;
    color: var(--primary-color);
}

h1 {
    font-size: 2.5rem;
}

h2 {
    font-size: 2rem;
    margin-top: 2rem;
}

h3 {
    font-size: 1.5rem;
    margin-top: 1.5rem;
}

p {
    margin-bottom: 1rem;
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color 0.3s ease;
}

a:hover {
    color: var(--accent-color);
}

.btn {
    display: inline-block;
    background-color: var(--accent-color);
    color: var(--light-text);
    padding: 0.75rem 1.5rem;
    border-radius: 4px;
    text-transform: uppercase;
    font-weight: bold;
    letter-spacing: 1px;
    transition: background-color 0.3s ease;
}

.btn:hover {
    background-color: #e91e63;
    color: var(--light-text);
}

/* Header */
header {
    background: linear-gradient(to right, var(--header-gradient-start), var(--header-gradient-end));
    color: var(--light-text);
    padding: 2rem 0;
    text-align: center;
}

header h1 {
    color: var(--light-text);
    margin-bottom: 0.5rem;
}

.subtitle {
    font-size: 1.2rem;
    opacity: 0.9;
}

/* Navigation */
nav {
    background-color: var(--primary-color);
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

nav ul {
    display: flex;
    list-style: none;
    justify-content: center;
    flex-wrap: wrap;
}

nav li {
    margin: 0;
}

nav a {
    display: block;
    color: var(--light-text);
    padding: 1rem 1.5rem;
    transition: background-color 0.3s ease;
}

nav a:hover {
    background-color: rgba(255, 255, 255, 0.1);
    color: var(--light-text);
}

/* Main Content */
main {
    padding: 2rem 0;
}

section {
    margin-bottom: 3rem;
    padding: 2rem;
    background-color: var(--card-background);
    border-radius: 8px;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.05);
}

.hero {
    background: url('../images/cosmic_distance_ladder.jpg') center/cover;
    color: var(--light-text);
    text-align: center;
    padding: 5rem 2rem;
    position: relative;
    border-radius: 8px;
    overflow: hidden;
}

.hero::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.6);
    z-index: 1;
}

.hero-content {
    position: relative;
    z-index: 2;
}

.hero h2 {
    color: var(--light-text);
    font-size: 2.5rem;
    margin-bottom: 1.5rem;
}

.hero p {
    font-size: 1.2rem;
    max-width: 800px;
    margin: 0 auto 2rem;
}

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

@media (min-width: 768px) {
    .module-content {
        grid-template-columns: repeat(2, 1fr);
    }
}

.unit {
    padding: 1.5rem;
    background-color: #f9f9f9;
    border-radius: 6px;
    border-left: 4px solid var(--secondary-color);
}

/* Images */
.image-container {
    margin: 1.5rem 0;
}

.responsive-img {
    max-width: 100%;
    height: auto;
    border-radius: 4px;
    display: block;
    margin: 0 auto;
}

.caption {
    font-size: 0.9rem;
    color: #666;
    text-align: center;
    margin-top: 0.5rem;
    font-style: italic;
}

/* Interactive Elements */
.interactive-element {
    margin: 2rem 0;
    padding: 1.5rem;
    background-color: #f0f0f0;
    border-radius: 6px;
    min-height: 200px;
    display: flex;
    align-items: center;
    justify-content: center;
}

/* Assessment */
.quiz-container {
    max-width: 800px;
    margin: 0 auto;
}

/* Footer */
footer {
    background-color: var(--primary-color);
    color: var(--light-text);
    padding: 2rem 0;
    text-align: center;
}

footer p {
    margin-bottom: 0.5rem;
}

/* Animations */
@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.fade-in {
    animation: fadeIn 1s ease-in;
}

/* Responsive Design */
@media (max-width: 768px) {
    h1 {
        font-size: 2rem;
    }
    
    h2 {
        font-size: 1.75rem;
    }
    
    h3 {
        font-size: 1.25rem;
    }
    
    nav ul {
        flex-direction: column;
    }
    
    nav a {
        padding: 0.75rem 1rem;
    }
    
    .hero {
        padding: 3rem 1rem;
    }
    
    .hero h2 {
        font-size: 2rem;
    }
}

@media (max-width: 480px) {
    .container {
        width: 95%;
        padding: 0 10px;
    }
    
    section {
        padding: 1.5rem;
    }
    
    .unit {
        padding: 1rem;
    }
}