#logo
{
position: relative;
width: 100px;
height: 18px;
float: right;
background-image: url('../images/logo_def.png');
background-repeat: no-repeat;
background-position: 50% 50%;
}
#logo a:hover
{
background-image: url(../images/logo_h.png);
}
它可以工作,但是当鼠标悬停在它上面时,bg-image 不会改变,为什么?