【children_parent】
<!DOCTYPE html>
<html>
<head>
<style type='text/css'>
#wr {
height: 400px;
width: 100%;
margin: 50px auto;
border: 1px solid black;
position: relative;
}
#con_top {
height: 40px;
margin: 5px;
border: 1px solid red;
background:#EEE;
}
#con_bottom {
background:#AAA;
border: 1px solid blue;
margin: 5px;
position: absolute;
top: 45px;
bottom: 0;
left: 0;
right: 0;
}
</style>
</head>
<body>
<div id="wr">
<div id="con_top"></div>
<div id="con_bottom"></div>
</div>
</body>
</html>
