header

main

css

    html, body, header, main, nav, footer {
        box-sizing: border-box;
        margin: 0;	
        padding: 0;
    }
    
    html{
         width: 100%;
         height: 100%; 
         background-color: lightgray;
    }
    
    body {
        width: 940px;
        height: 100%; 
        margin: 0 auto;
        background: antiquewhite;
    }
    
    header{
        width: 100%;
        height: 100px;
        padding: 1rem;
        text-align: center;
        background: orange;
        color: green;
    }
    
    header h1{
        margin: 0;
        padding-top: 0.5rem;
    }
    
    main{ 
        padding: 1rem;
        float: right; 
        width: 80%;
        height: calc(100% - 100px - 2rem); 
        overflow: auto;
    }
    
    nav{ 
        float: left; 
        width: 20%;
        height: calc(100% - 100px - 2rem); 
        overflow: auto;
        border-right: solid 1px gray;
        padding: 1rem;
    }
    
    footer{
        clear: both;
        width: 100%;
        height: 2rem;
        padding-top: 0.5rem;
        text-align: center;
        color: white;
        background: green;
    }