<!DOCTYPE html> <!-- Any copyright is dedicated to the Public Domain. - http://creativecommons.org/publicdomain/zero/1.0/ --> <html> <style> summary::-moz-list-bullet { /* Hide the triangle for comparing with div in reftest. */ list-style-type: none; } summary { -moz-column-count: 3; -moz-column-rule: 1px solid lightgray; -webkit-column-count: 3; -webkit-column-rule: 1px solid lightgray; border: 1px solid lightblue; background-color: lightgreen; } </style> <body> <details open> <summary> <p>line</p> <p>line</p> <p>line</p> <p>line</p> <p>line</p> <p>line</p> <p>line</p> </summary> <p>This is the details.</p> </details> </body> </html>