用之前讲的position为什么不行呢？
#mainbody {
background:#FC0;
width:100%;
position:relative;
top:0;
left:0;
}
.left {
width:800px;
height:200px;
background:#000;
position:absolute;
top:0;
left:0;
}
.right {
width:140px;
height:500px;
background:#690;
position:absolute;
top:0;
right:0;
}
