Edit in JSFiddle

<div class="parent">
<div class="left"><p>left</p></div>
<div class="right"><p>right</p>
<p>right</p>
<p>right</p></div>
</div>

@mixin common {
  text-align: center;
  color: white;
}

.parent {
  @include common;
  overflow: hidden;
  .left{
    background-color: red;
    float: left;
    padding-bottom: 9999px;
    margin-bottom: -9999px;
  }
  .right{
    background-color: blue;
    overflow: hidden;
    padding-bottom: 9999px;
    margin-bottom: -9999px;
  }
}