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chromium/third_party/blink/web_tests/fast/multicol/vertical-lr/column-break-with-balancing.html 

<!DOCTYPE html>
<style>
    body {
        -webkit-writing-mode: vertical-lr;
    }
    .columns {
        height: 400px;
        width: 200px;
        -webkit-column-width: 200px;
        -webkit-column-gap: 0;
        border: 5px solid blue;
        margin-right: 1em;
        line-height: 20px;
    }
</style>
<div class="columns">
    First column<br>
    First column<br>
    First column<br>
    First column<br>
    First column<br>
    First column<br>
    First column<br>
    First column<br>
    First column<br>
    First column<br>
    <div style="-webkit-column-break-before: always">
        Second column<br>
        Second column<br>
        Second column<br>
        Second column<br>
    </div>
</div>
<div class="columns">
    First column<br>
    First column<br>
    First column<br>
    First column<br>
    <div style="-webkit-column-break-before: always">
        Second column<br>
        Second column<br>
        Second column<br>
        Second column<br>
        Second column<br>
        Second column<br>
        Second column<br>
        Second column<br>
        Second column<br>
        Second column<br>
    </div>
</div>