body {
    font-family: sans-serif;
    background-color: lightgray;
}

#all {
    background-color: white;
    width: 600px;
    margin-left: auto;
    margin-right: auto;
}

header {
    text-align: center;
}

nav {
    background-color: green;
    float: left;
    width: 150px;
    color: white;
    height: 400px;
}

#content {
    background-color: yellow;
    float: left;
    width: 440px;
    height: 400px;
    padding-left: 10px;
}

footer {
    color: white;
    background-color: gray;
    clear: both;
    text-align: center;
}