Having started with T312933 and T312970 related to #wikieditor, I discovered that quite many MediaWiki parts and extensions don't respect the default browser font size, setting an absolute `font-size` in `px` instead of relative in `em`/`rem`. I'm not sure whether I should create an individual task for every finding because there's quite a few of them, their list is likely to grow, and they are typical.
Here's what I stumbled upon as of now:
* #page-previews have a fixed `font-size` of `14px`. Here's how they look in Firefox with `20px` as the default font size:
{F35320488}
* Diffs are rigidly set to `13px`. That's their look:
{F35320491}
* `#siteSub` is strictly `12.8px`. Here's how it looks like:
{F35320496}
* `line-height` in `.sidebar-toc` is exactly `18px`. It may be not obvious what's so bad but here's the difference with `16px` as the default size:
| {F35320500} | {F35320502}
Related task: {T27257}