chromium/third_party/blink/web_tests/fast/multicol/overflow-content.html

<style>
    div.test {
        inline-size: 100px;
        border-block-start: 5px solid;
        border-block-end: 15px solid;
        -webkit-column-count: 2;
        -webkit-column-gap: 0;
        column-count: 2;
        column-gap: 0;
        column-fill: auto;
        background-color: lightblue;
    }
    div.container {
        block-size: 120px;
        background-color: red;
        inline-size: 100px;
        margin-block-end: 8px;
    }
</style>
<div>
    <div class="container">
        <div class="test" style="block-size: 100px;">
            <div style="block-size: 20px;">
                <div style="block-size: 300px; background-color: yellow;"></div>
            </div>
        </div>
    </div>

    <div class="container">
        <div class="test">
            <div style="block-size: 20px;">
                <div style="block-size: 200px; background-color: yellow;"></div>
            </div>
        </div>
    </div>

    <div class="container">
        <div class="test">
            <div style="block-size: 10px;"></div>
            <div style="-webkit-column-break-before: always; block-size: 10px;">
                <div style="block-size: 100px; background-color: yellow;"></div>
            </div>
            <div style="block-size: 20px;"></div>
        </div>
    </div>
</div>
<div style="-webkit-writing-mode: vertical-rl;">
    <div class="container">
        <div class="test" style="block-size: 100px;">
            <div style="block-size: 20px;">
                <div style="block-size: 300px; background-color: yellow;"></div>
            </div>
        </div>
    </div>

    <div class="container">
        <div class="test">
            <div style="block-size: 20px;">
                <div style="block-size: 200px; background-color: yellow;"></div>
            </div>
        </div>
    </div>

    <div class="container">
        <div class="test">
            <div style="block-size: 10px;"></div>
            <div style="-webkit-column-break-before: always; block-size: 10px;">
                <div style="block-size: 100px; background-color: yellow;"></div>
            </div>
            <div style="block-size: 20px;"></div>
        </div>
    </div>
</div>