按钮偏移换图

.submit {
border:0px;
width: 110px;
height: 40px;
background-color:yellow;
background: url(../images/login/btn.png);
font-size: 20px;
margin:20px 10px 0px;
}
.submit:hover {
width: 110px;
height: 40px;
color: #FFFFFF;
background: url(../images/login/btn.png) 0 -40px ;
}