ul {
    margin-left: 5em;
    list-style: none; 
}
li {
    padding-left: 50px; 
    
    background-image: url("lolアイコン.jpg");
    background-repeat: no-repeat;    
    background-position: left center; 
    
    background-size: 50px 50px; 
}

li:hover {
    background-image: url("アイコン.jpg");
}

li:active {
    background-image: url("アイコン2.jpg");
}