html .expandable.open {
    background-image: url("https://energy.stanford.edu/sites/default/files/images/arrow_down.png");
    background-position: left center;
    padding-left: 15px;}
html .expandable {
    background-image: url("https://energy.stanford.edu/sites/default/files/images/arrow_right.png");
    background-position: left center;
    background-repeat: no-repeat;
    padding-left: 15px;}