//原样式
li {
float: left;
width: 250px;
background: #fff;
margin-left: 2px;
margin-bottom: 2px;
height: 140px;
position: relative;
overflow: hidden;
}
li:before {
content: "";
position: absolute;
z-index: 0;
width: 251px;
height: 140px;
left: 50%;
top: 50%;
margin-left: -125px;
margin-top: -70px;
opacity: 0;
-webkit-transition: .5s cubic-bezier(.3, 0, 0, 1.3);
-moz-transition: .5s cubic-bezier(.3, 0, 0, 1.3);
-ms-transition: .5s cubic-bezier(.3, 0, 0, 1.3);
-o-transition: .5s cubic-bezier(.3, 0, 0, 1.3);
transition: .5s cubic-bezier(.3, 0, 0, 1.3);
-webkit-transform: scale(0, 0);
-moz-transform: scale(0, 0);
-ms-transform: scale(0, 0);
-o-transform: scale(0, 0);
transform: scale(0, 0);
background-color: #83c325;
}
//hover样式 通过:before放大来实现背景从内向外辐射改变
li:hover:before {
opacity: 1;
-webkit-transform: scale(1, 1);
-moz-transform: scale(1, 1);
-ms-transform: scale(1, 1);
-o-transform: scale(1, 1);
transform: scale(1, 1);
}