<div>
  <div class="left">float element / no fixed width</div>
  <div class="right">adaptive</div>
</div>
* {
  margin: 0;
  padding: 0;
}

.left {
  float: left;
  height: 200px;
  margin-right: 10px;
  background-color: skyblue;
}

.right {
  height: 200px;
  background-color: pink;
}
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