<div class="header">
<div class="layout">头部</div>
</div>
<div class="main layout">内容</div>
<div class="footer"></div>
.header {
background: blue;
height: 80px;
}
.main {
background: red;
height: 500px;
}
.footer {
background: green;
height: 80px;
}
.layout {
width: 960px;
margin: 15px auto;
border: 3px solid black;
}
如何实现内容区域高度自动填充到底部?