<html class="reftest-wait"> <head> <style> body { width: 100px; line-height: 15px; } div { width: 100px; float: left } div.a { height: 30px; background: lightblue; } div.b { height: 10px; background: lightgreen; } div.c { height: 10px; background: black; } </style> <script> function tweak() { document.getElementById('changeMe').style.height = '100px'; document.documentElement.className = ""; } </script> </head> <body onload="tweak()"> <div class="a"></div> <div class="b" id="changeMe"></div> <div class="c"></div> </body> </html>