<style>
.container {
  width: 100px;
}
.left {
  width: 50px;
  height: 50px;

  float: left;
  background-color: green;
}
.right {
  width: 50px;
  height: 50px;

  /* 100% of the 100px container */
  margin-left: 100%;
  overflow: hidden;
  background-color: blue;
}
</style>
<div class=container>
  <div class=left></div>
  <div class=right></div>
</div>
