*{
  margin:0;
  padding:0
}
body, html, .body{
  height:100%;
  width:100%;
}
.body{
  display: flex;
  flex-direction: column;
}
.box1{
  display: flex;
  justify-content: space-between;
  align-items: center;
  height:50px;
  line-height:50px;
  background:red;
  color:#fff;
}
.content{
  display: flex;
  flex: 1;
  overflow-y: auto;
}
.footer{
  height:50px;
  line-height: 50px;
  background:blue;
  text-align: center;
}
.header1, .header3{
  width:10%;
  vertical-align: middle;
  line-height: 50px;
  text-align: center;
}
.header2{
  width:80%;
  text-align: center;
}
 
html
<div class="body">
  <div class="box1">
    <div class="header1"><</div>
    <div class="header2">容</div>
    <div class="header3"></div>
  </div>
  <div class="content">内容</div>
  <div class="footer">底部</div>
</div>