.chinaz { width: 100%; height: 450px; max-height:100%;position: relative; overflow:hidden;}
.chinaz img{
    vertical-align: top;
}

.chinaz .prev,.chinaz .next {
    display: none;
    width: 40px;
    height: 100px;
    background: url(../images/btn.png) no-repeat;
    position: absolute;
    top:35%;
}

.chinaz .prev {
    left: 0;
}
.chinaz .next {
    right: 0;
    background-position: right
}