<!DOCTYPE html>
<style>
    body {
        -webkit-writing-mode: vertical-rl;
    }
    .multicol {
        height: 480px;
        width: 200px;
        border: 3px solid black;
        -webkit-column-gap: 0;
        -webkit-column-count: 3;
        line-height: 20px;
    }
    .float {
        padding: 10px;
        background-color: skyblue;
    }
    .left { float: left; }
    .right { float: right; }
</style>
<div class="multicol">
    First<br>
    First<br>
    First<br>
    First<br>
    <div class="float left">L1</div>
    <div class="float right">R1</div>
    First<br>
    First<br>
    First<br>
    First<br>
    First<br>
    First<br>

    <div class="float left">L2</div>
    <div class="float right">R2</div>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>
    Second<br>

    Third<br>
    Third<br>
    Third<br>
    Third<br>
    Third<br>
    Third<br>
    Third<br>
    Third<br>
    <div class="float left">L3</div>
    <div class="float right">R3</div>
    Third<br>
    Third<br>
</div>