.navs {
    position: absolute;
    width: 1000px;
    left: 50%;
    margin-left: -500px;
    top: 930px;
    text-align: center;
}
.navs a {
    display: inline-block;
    margin-left: 30px;
    margin-right: 30px;
}
.navs a:hover {
}

.nav1,
.nav2,
.nav3,
.nav4 {
    width: 236px;
    height: 158px;
}
.nav1 {
    background: url(../image/b1.png) bottom center no-repeat;
}

.nav2 {
    background: url(../image/b2.png) bottom center no-repeat;
}
.nav3 {
    background: url(../image/b3.png) bottom center no-repeat;
}
.nav4 {
    background: url(../image/a4.png) bottom center no-repeat;
}

.nav1:hover,
.nav2:hover,
.nav3:hover,
.nav4:hover {
    cursor: pointer;
    background-position: top center;
}

.nav1:hover {
    background-position: center 30px;
}
.nav3:hover {
    background-position: center 30px;
}