Thanks! We do test things repeatedly (both using automated tests and manual/visual tests) while we're working on them, and these particular changes were tested by multiple people with different systems/devices/browsers. It's not feasable for us to visually test every style and theme on the site, though -- there's a lot of them, well over a thousand last time I checked -- so the sort of issues that don't get caught by automated testing will always sneak through. And although we aim for as wide a variety of systems/devices/browsers in testing as we can, everyone who visits the site has a slightly different setup due to browser version, browser settings, extensions installed, etc, so any design or CSS changes inevitably need a bunch of after-the-fact fixes when they meet the real world (much wider) set of configurations.

I'm sorry for the hassle! Ultimately these changes are to modernize a bit of the code that was really, really old and janky so that we can support mobile browsers better, since usability on mobile (and other small-viewport devices) is people's #1 most-cited issue right now. But, because the code in question is literally 20 years old and had layers and layers of "wtf" lurking in it, we had to strip it down pretty far to make any progress and then rebuild on the new bones, so it'll take us a few rounds of fixes to shake out all the issues that only show up once changes hit the real-world panopoly of people's configs. We will get it all fixed!