/* Global Variables */
:root {
    /* Color Palette */
    --primary-color: #2a3b4d;
    --secondary-color: #5c7c9c;
    --accent-color: #f5b301;
    --success-color: #4CAF50;
    --text-color: #333333;
    --bg-color: #f8f9fa;
    --card-bg: #ffffff;
    --border-color: #e0e0e0;

    /* Spacing */
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 2rem;
    --spacing-xl: 4rem;

    /* Shadows */
    --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
}

/* Dark Mode Support (System preference) */
/* Dark Mode Support Removed to enforce Light Mode */
/*
@media (prefers-color-scheme: dark) {
    :root {
        --primary-color: #1a2633;
        --secondary-color: #4a6b8c;
        --text-color: #f0f0f0;
        --bg-color: #121212;
        --card-bg: #1e1e1e;
        --border-color: #333;
    }
}
*/

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

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--bg-color);
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

a {
    text-decoration: none;
    color: inherit;
    transition: color 0.3s ease;
}

ul {
    list-style: none;
}

/* Layout Utilities */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

/* Header & Navigation */
.main-header {
    background-color: var(--card-bg);
    box-shadow: var(--shadow-sm);
    padding: var(--spacing-md) 0;
    position: sticky;
    top: 0;
    z-index: 1000;
}

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

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
}

.nav-list {
    display: flex;
    gap: var(--spacing-lg);
}

.nav-link {
    color: var(--primary-color);
    font-weight: 500;
}

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

/* Component: Buttons */
.btn {
    display: inline-block;
    padding: 0.8rem 1.5rem;
    border-radius: 6px;
    border: none;
    cursor: pointer;
    font-weight: 600;
    text-align: center;
    transition: all 0.3s ease;
}

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

.btn-primary:hover {
    background-color: var(--secondary-color);
    transform: translateY(-2px);
}

.btn-simulation {
    background-color: var(--success-color);
    color: white;
    width: 100%;
}

.btn-simulation:hover {
    background-color: #43a047;
}

/* Component: Cards */
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.card {
    background: var(--card-bg);
    padding: var(--spacing-lg);
    border-radius: 12px;
    box-shadow: var(--shadow-sm);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    border: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.card h3 {
    color: var(--secondary-color);
    margin-bottom: var(--spacing-md);
}

/* Utility: Math Formulas */
.formula-box {
    background-color: rgba(0, 0, 0, 0.05);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: 4px;
    font-family: 'Courier New', monospace;
    margin: var(--spacing-sm) 0;
    display: inline-block;
    border-left: 3px solid var(--secondary-color);
}

/* Footer */
.main-footer {
    background-color: var(--primary-color);
    color: white;
    text-align: center;
    padding: var(--spacing-lg);
    margin-top: auto;
}

.main-footer a {
    color: var(--secondary-color);
}

/* Responsive */
@media (max-width: 768px) {
    .nav-list {
        display: none;
        /* TODO: Add mobile menu toggle */
    }

    .hero h1 {
        font-size: 2rem;
    }
}

/* Page Specific: Hero (Index) */
.hero-section {
    background-image: url('../image/img_4.jpeg');
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    padding: 100px 20px;
    color: white;
    text-align: center;
    /* Overlay to improve text readability */
    box-shadow: inset 0 0 0 1000px rgba(0, 0, 0, 0.4);
}

.hero-section h1 {
    font-size: 3rem;
    font-weight: 300;
    margin-bottom: 1.5rem;
    color: white;
    /* Override primary color */
}

.hero-section p {
    font-size: 1.25rem;
    max-width: 800px;
    margin: 0 auto 2rem;
    color: #f0f0f0;
}

/* Sections */
.section-title {
    font-size: 2rem;
    font-weight: 400;
    margin-bottom: 2rem;
    color: var(--primary-color);
    text-align: center;
    margin-top: var(--spacing-xl);
}