chromium/third_party/blink/web_tests/fast/multicol/column-rules.html

<!DOCTYPE html>
<style>
    .multicol {
        width: 470px;
        -webkit-columns: 3;
        -webkit-column-rule: 4px solid maroon;
        -webkit-column-gap: 10px;
        padding: 0 10px;
        border: 5px solid black;
        line-height: 20px;
    }
</style>
<div class="multicol">
    Line 1<br>
    Line 2<br>
    Line 3<br>
    Line 4<br>
    Line 5<br>
    Line 6<br>
    Line 7<br>
    Line 8<br>
    Line 9<br>
    Line 10<br>
    Line 11<br>
    Line 12<br>
    Line 13<br>
    Line 14<br>
    Line 15<br>
    Line 16<br>
    Line 17<br>
    Line 18<br>
    Line 19<br>
    Line 20<br>
    Line 21<br>
    Line 22<br>
    Line 23<br>
    Line 24<br>
    Line 25<br>
    Line 26<br>
    Line 27<br>
    Line 28<br>
    Line 29<br>
    Line 30<br>
</div>