$sidebar_width: 20%;

body {
    margin: 0;
    nav {
        height: 100%;
        position: fixed;
        width: $sidebar_width;
        background: rgba(255, 0, 0, .1);
        padding-top: 32px;
        img {
            width: 100%;
        }
        div {
            padding: 0 16px 0 16px;
        }
    }
    main {
        height: 100%;
        margin-left: $sidebar_width;
        background: rgba(0, 255, 0, .1);
        padding-top: 50px;
        article {
            margin: auto;
            border: 1px solid blue;
            padding: 16px;
            max-width: 1000px;
        }
    }
}