<!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>