.om-list > ul > li {
    position: relative;
    padding-left: 5px;
}
.om-list > ul > li:before {
    content: '';
    position: absolute;
    width: 20px;
    height: 20px;
    left: -25px;
    top: 10px;
    background-image: url(png/om.png);
    background-size: contain;
}