body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background-color: #f4f4f4;
}

header {
    background-color: #333;
    color: white;
    padding: 10px 0;
}

nav ul {
    list-style-type: none;
    padding: 0;
}

nav ul li {
    display: inline;
    margin: 0 10px;
}

nav ul li a {
    color: white;
    text-decoration: none;
}

main {
    text-align: center;
    margin: 10px auto;
    max-width: 1200px;
}

.columns {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
}

.column {
    flex: 1;
    padding: 10px;
    max-width: 500px;
}

.video {
    background-color: #fff;
    padding: 10px;
    margin-bottom: 20px;
    border-radius: 5px;
    box-shadow: 0 0 10px rgba(0,0,0,0.1);
}

iframe, video {
    width: 100%;
    height: auto;
    max-width: 560px;
}

@media (max-width: 768px) {
    .columns {
        flex-direction: column;
    }
}