.left .left_down li.a.left-down-pic{
display:block;
50px;
height:50px;
background:url(images/app_icons_50_6.jpg) -400px 0px no-repeat;//关键是这句话
}
.left .left_down li.a.left-down-pic{
display:block;
50px;
height:50px;
background:url(images/app_icons_50_6.jpg) -400px 0px no-repeat;//关键是这句话
}