<!DOCTYPE html>
<html>
    <head>
        <title>hiding a box covering a multicol, horizontal-bt</title>
    </head>
    <body>
        <p>The word PASS should be seen below.</p>
        <div style="position:relative; background:lime;">
            <div style="position:absolute; z-index:1; left:0; right:0; top:0; height:6em; background:white;"></div> <!-- make it fail if writing-mode isn't supported  -->
            <div style="width:20em; height:20em; -webkit-writing-mode:horizontal-bt;">
                <div style="-webkit-columns:4; -webkit-column-fill:auto; -webkit-column-gap:0; columns:4; column-fill:auto; column-gap:0; orphans:1; widows:1; height:6em; line-height:2em; background:cyan;">
                    <br>
                    <br>
                    <br>
                    <br>
                    &nbsp;PASS
                </div>
            </div>
        </div>
    </body>
</html>