body {
    font-family: 'Roboto', sans-serif;
    background-color: #222;
    color: #fff;
    margin: 0;
    padding: 0;
}

header {
    background-color: #333;
    padding: 20px;
    text-align: center;
}

main {
    padding: 20px;
}

#challenges {
    margin-bottom: 30px;
}

.challenge-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 20px;
}

.challenge-card {
    background-color: #444;
    padding: 20px;
    text-align: center;
    border-radius: 5px;
    text-decoration: none;
    color: #fff;
    display: block;
}

.challenge-card:hover {
    background-color: #555;
}

footer {
    background-color: #333;
    padding: 20px;
    text-align: center;
}