<div class="box">
    <div class="left">左边</div>
    <div class="center">中间</div>
    <div class="right">右边</div>
</div>
.box{
  display: flex;
  min-width:550px;
}
.left{
  width:200px;
  height: 200px;
  background:red;
}
.center{
  flex: 1;
  background: yellow;
}
.right{
  width: 200px;
  height:200px;
  background:blue;
}
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