<!doctype HTML>
<style>
.sized {
    width: 100px;
    height: 20px;
}
.blue {
    background: lightblue;
}
.green {
    background: green;
}
</style>
<div id=target style="border-radius: 10px; overflow: hidden; height: 100px; width: 600px; column-count: 2;">
    <div class="sized blue"></div>
    <div class="sized blue"></div>
    <div class="sized blue"></div>
    <div class="sized blue"></div>
    <div class="sized blue"></div>
    <div class="sized green"></div>
</div>