<!DOCTYPE html>
<style>
    body {
        -webkit-writing-mode: vertical-lr;
    }
    .multicol {
        height: 330px;
        width: 200px;
        border: 3px solid #bbb;
        -webkit-column-gap: 10px;
        -webkit-column-count: 2;
        line-height: 20px;
    }
    .left, .right {
        padding: 5px 5px;
        background-color: steelblue;
    }
    .float_content {
        background-color: skyblue;
    }
    .left { float: left; }
    .right { float: right; }
</style>
<div class="multicol">
    First<br>
    First<br>
    First<br>
    First<br>
    <div class="left">
        <span class="float_content">
            left1<br>
            left2<br>
            left3<br>
            left4<br>
            left5<br>
            left6<br>
            left7<br>
        </span>
    </div>
    <div class="right">
        <span class="float_content">
            right1<br>
            right2<br>
            right3<br>
            right4<br>
            right5<br>
            right6<br>
            right7<br>
        </span>
    </div>
    First<br>
    First<br>
    First<br>
    First<br>
    First<br>
    First<br>


    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
</div>