上下布局：下面固定高度，下面自适应
<style>
html, body {
height: 100%;
margin: 0;
padding: 0;
}
.div1 {
position: relative;
height: 60%;
width: 500px;
background: lightblue;
}
.div1_1 {
width: 100%;
height: 50px;
background: lightcoral;
}
.div1_2 {
position: absolute;
top: 50px;
bottom: 0;
width: 80%;
background: lightgrey;
overflow: auto;
}
.div1_2_1 {
height: 1000px;
}
</style>
<div class="div1">
<div class="div1_1"></div>
<div class="div1_2">
<div class="div1_2_1"></div>
</div>
</div>
