Whoops, I figured the full file was simple enough I probably wouldn't need to check in Safari or Chrome (yeah, learnt my lesson I guess). Turned out there were a few weird issues with colours, transitions, and sizes (mostly to do with SVG images like the menu icons and example pages). I've made the following changes and the full file should now look fine in Chrome, Safari, and Firefox.

Here are the main changes:

• the smooth transition between themes is gone (I might come back to it, but I wanted to get an updated version out first)
• the menu bar controls now fit into the menu bar in Chrome and Safari
• the skip link should now be fully out of the way under all settings
• the 2-column layouts in the menu tabs are less cramped