:root {
    --primary-color: #2c3e50;
    --accent-color: #27ae60;
    --bg-color: #f4f6f7;
    --card-bg: #ffffff;
    --text-color: #333;
}

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

header {
    background-color: var(--primary-color);
    color: white;
    padding: 1rem 0;
    text-align: center;
}

.container {
    width: 80%;
    margin: 2rem auto;
    max-width: 1200px;
}

.hero {
    text-align: center;
    padding: 3rem 1rem;
    background: var(--card-bg);
    border-radius: 8px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
    margin-bottom: 2rem;
}

.hero h1 {
    margin-top: 0;
    color: var(--primary-color);
}

.concepts-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
}

.card {
    background: var(--card-bg);
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.05);
    transition: transform 0.2s;
    border-top: 4px solid var(--accent-color);
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
}

.card h3 {
    margin-top: 0;
    color: var(--primary-color);
}

.badge {
    background-color: var(--accent-color);
    color: white;
    padding: 0.2rem 0.5rem;
    border-radius: 4px;
    font-size: 0.8rem;
    text-transform: uppercase;
}

footer {
    text-align: center;
    padding: 2rem 0;
    color: #777;
    margin-top: 2rem;
}