/* Global Styles */
:root {
    --bg-color: #f4f7f6;
    --text-color: #333333;
    --card-bg: #ffffff;
    --nav-bg: #2c3e50;
    --nav-text: #ffffff;
    --accent-color: #3498db;
    --border-color: #e0e0e0;
}

[data-theme="dark"] {
    --bg-color: #1a1a1a;
    --text-color: #f5f5f5;
    --card-bg: #2d2d2d;
    --nav-bg: #111111;
    --nav-text: #ffffff;
    --accent-color: #1abc9c;
    --border-color: #444444;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    margin: 0;
    padding: 0;
    background-color: var(--bg-color);
    color: var(--text-color);
    transition: background-color 0.3s, color 0.3s;
    line-height: 1.6;
}

header {
    background-color: var(--nav-bg);
    color: var(--nav-text);
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: sticky;
    top: 0;
    z-index: 1000;
}

.logo {
    font-size: 1.5rem;
    font-weight: bold;
}

nav a {
    color: var(--nav-text);
    text-decoration: none;
    margin-left: 1.5rem;
    font-weight: 500;
    transition: color 0.2s;
}

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

.theme-toggle {
    background: none;
    border: 2px solid var(--accent-color);
    color: var(--accent-color);
    padding: 0.5rem 1rem;
    border-radius: 20px;
    cursor: pointer;
    font-weight: bold;
    transition: all 0.3s;
}

.theme-toggle:hover {
    background-color: var(--accent-color);
    color: #fff;
}

main {
    max-width: 1000px;
    margin: 2rem auto;
    padding: 0 1rem;
}

.container {
    background-color: var(--card-bg);
    padding: 2rem;
    border-radius: 8px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
    border: 1px solid var(--border-color);
}

h1, h2, h3 {
    color: var(--accent-color);
}

/* Timeline for History */
.timeline {
    position: relative;
    max-width: 100%;
    margin: 2rem auto;
    padding-left: 2rem;
    border-left: 4px solid var(--accent-color);
}

.timeline-item {
    margin-bottom: 2rem;
    position: relative;
}

.timeline-item::before {
    content: '';
    position: absolute;
    left: -2.35rem;
    top: 0.25rem;
    background-color: var(--bg-color);
    border: 4px solid var(--accent-color);
    width: 12px;
    height: 12px;
    border-radius: 50%;
}

.timeline-year {
    font-weight: bold;
    font-size: 1.2rem;
    color: var(--accent-color);
}

/* Cards Grid for Methods and Types */
.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
    margin-top: 1.5rem;
}

.card {
    background-color: var(--bg-color);
    padding: 1.5rem;
    border-radius: 6px;
    border: 1px solid var(--border-color);
}

footer {
    text-align: center;
    padding: 2rem;
    margin-top: 4rem;
    font-size: 0.9rem;
    border-top: 1px solid var(--border-color);
}