body {
    font-family: Arial, sans-serif;
}
#banner-ad {
    height: 150px;
    background-color: #ddd;
    text-align: center;
    line-height: 100px;
}
header {
    background-color: #f2f2f2;
    text-align: center;
    padding: 20px 0;
}
header h1 {
    margin: 0;
    font-size: 2em;
}
header p {
    margin: 0;
    font-style: italic;
}
nav ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #333;
}
nav li {
    float: left;
}
nav li a {
    display: block;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
}
nav li a:hover {
    background-color: #111;
}
#sidebar {
    width: 200px;
    float: right;
    background-color: #f2f2f2;
    padding: 10px;
}
#content {
    margin-left:25px;
    margin-right: 220px; /* Sidebar width + padding */
}
footer {
    clear: both;
    background-color: #f2f2f2;
    text-align: center;
    padding: 20px 0;
}
@media screen and (max-width: 600px) {
    #sidebar {
        display: none;
    }
    #content {
        margin-right: 0;
    }
    nav li {
        float: none;
    }
}