Having a browser-based application is odd in so many ways, this being one of them. Obviously when we make the design/functionality for the site, we design it around a set of core assumptions, one of which is, for example, the "base" font size. Browsers allow the end-user to override almost anything, though, which is nice and probably works quite well for an average mostly text site, like an article or a blog, but it can also wreak havoc with complicated apps like Roll20. For example, zooming in the text will cause the right-sidebar tabbed navigation to lose buttons sometimes. So it's not really a bug, it's just something we haven't "tested"/"supported" (changing the base font size via your end-user CSS overrides). I'm not sure that it even is something we can support -- after all, what if someone increases the font size to 26? Or decreases it to 9? What if they change their CSS so all text has a 2px drop shadow or all tables display with a 1px black border? These are all things you can do via browsers, but as you can see we can't possibly test every scenario, just like we can't support people who run addons on top of their browser's base functionality that break things in Roll20. So, please feel free to change anything you'd like about the way Roll20 displays in your browser, I just can't guarantee it won't cause something else to break :-) That said, perhaps in the future we can offer an option to increase the font size of the chat log via an official setting...
