<!DOCTYPE html>
<html>
    <head>
        <title>hiding a box covering a multicol, vertical-rl</title>
    </head>
    <body style="color:black; background:white;">
        <p>The word PASS should be seen below.</p>
        <div style="position:relative; width:30em; background:black;">
            <div style="width:20em; height:20em; -webkit-writing-mode:vertical-rl;">
                <div style="block-size:6em; line-height:2em; background:cyan;">
                    <br>
                    <span style="margin-inline-start:5em;">&nbsp;PASS</span>
                </div>
            </div>
        </div>
    </body>
</html>