图片没有完全覆盖poster-main，而是往下移了一小截

一下是css代码

.poster-main{

position:relative;

width:840px;

height:270px;

background-color:red;

}

.poster-main a img{

display:block;

}

.poster-main .poster-list{

width:800px;

height:270px;

}

.poster-main .poster-list .poster-item{

position:absolute;

left:0;

top:0;

}

.poster-main .poster-btn{

position:absolute;

top:0;

width:100px;

height:270px;

z-index:10;

background-color:red;

}

.poster-main .poster-prev-btn{

left:0;

}

.poster-main .poster-next-btn{

right:0;

}