Edit in JSFiddle

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

@mixin common {
  line-height: 100px;
  height: 100px;
  text-align: center;
  color: white;
}

.parent {
  @include common;
  .left {
    background-color: red;
    float: left;
  }
  .right {
    background-color: blue;
    overflow: hidden;
  }
}