Using the :before property to create a retina ready alternate colour disc in an unordered list

gistfile1.txt

ul {
    padding: 5px 0 10px;
    margin: 0;
    position: relative;
        li {
            padding: 0 0 10px 15px;
            &:before {
                content: "•";
                position: absolute;
                left: 0px;
                font-size: 21px;
                color: #444;
            }
        }
    }