gistfile1.sass

.content-panel__bg {
        z-index: -1;
        position: absolute;
        top: 0; left: 0;
        width: 100%; height: 100%;
        
        // http://css-tricks.com/full-browser-width-bars/
        &:before, &:after {
            content: "";
            position: absolute;
            top: 0; bottom: 0;
            // needs background from --*colour* modifier
            background: white;
            width: 9999px;
        }
        
        &:before {
            right: 100%;
        }
        
        &:after {
            left: 100%;
        }
}

.content-panel--teal {
        .content-panel__bg {
            background: $teal;

            &:before, &:after {
                background: $teal;
            }
        }
}