css
span{
width: 20px;
height: 20px;
display: block;
background-image: url(图片url);
transition: .2s ease-in-out;
-webkit-transition: .2s ease-in-out;
-moz-transition: .2s ease-in-out;
-o-transition: .2s ease-in-out;
}
span:hover{
transform: rotate(-180deg);
-webkit-transform: rotate(-180deg);
-moz-transform: rotate(-180deg);
-o-transform: rotate(-180deg);
}
html
<span></span>