body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
}

header {
    font-size: 15px;
    text-align: center;
}

nav {
    font-size: 20px;
    text-align: center;
}

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

nav li {
    display: inline;
    margin-right: 20px;
}

.main {
    width: 80%;
}

.container {
    position: relative;
    padding-bottom: 76.25%;
    height: 0;
    overflow: hidden;
}

iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 80%;
    height: 100%;
}

@media only screen and (max-width: 768px) {
    nav {
        font-size: 20px;
    }
}