demo.css

    body {
        margin: 0;
        font: 100%/1.5 Geneva, Segoe UI, Helvetica, sans-serif;
    }
    
    h1, h2, h3, h4, h5, h6 {
        font-family: Didot, "Didot LT STD", Bodoni MT, "Hoefler Text", Garamond, "Times New Roman", serif
    }
    
    main {
        padding: 1em calc(50vw - 500px);
    }
    
    
            foo {
                background: black;
            }