<!DOCTYPE html>
<style>
.columns {
border:2px solid black;
height:300px;
}
.block {
width: calc(50% - 10px);
height: 200px;
background-color:purple;
}
.left { float: left; }
.right { float: right; }
</style>
The two purple rectangles below should both be at the top of their columns. If one is lower than the other, than the test has failed.
<div class="columns">
<div class="block left"></div>
<div class="block right"></div>
</div>