求助！！明天交作业了

html如下
<div id="zhuti">
<div id="xiangqing"><a href="main.html">查看详细>></a></div>
<div id="shi1"><video src="20180110083312.mp4" width="1500px" autoplay loop></video></div>
<div id="shi2"><video src="20180110083502.mp4" width="1500px" autoplay loop></video></div>
<div id="dibu1">< </div><div id="dibu2">> </div>
</div>

css如下
#shi1{
position:relative;
top:-14px;
left:-100px;
}
#shi2{
position:absolute;
top:405px;
left:199px;
display:none;
}
#dibu1:hover shi2{
display:block;
}
#dibu1{
height:100px;
width:50px;
background:#0CC;
opacity:0.4;
border-radius:20%;
position:relative;
top:-350px;
left:-100px;
z-index:999989;
font-size:36px;
text-align:center;
line-height:100px;
}

很急很急 我看了好久了 没看出来哪里做错了 刚学html小白别喷我。