简单实现页面“自适应”样式，小技巧！！！

*{
box-sizing: border-box;
-webkit-box-sizing: border-box;
}

html,body{
height: 100%;
}

.header{
background: red;
height: 140px;
margin-bottom: -140px;
position: relative;
}

.mid_content{
background: gold;
min-height: 100%;
padding: 140px 0px 150px 0px;
}

.footer{
background: blanchedalmond;
height: 150px;
margin-top: -150px;
}