Edit in JSFiddle

<div class="father">
    <div class="left">左</div>
    <div class="right">右</div>
</div>

html,body{margin:0; padding: 0;}
.father{
  display:flex;
}
.father .left,.father .right { 
  height: 200px; 
  line-height:200px; 
  text-align:center; }
  
.father .left{width:200px; background-color:#FAD7F0; }
.father .right{ background-color:#C7DAFC; flex:1;}