Hi Evan, welcome to the forum.
Zenrain is the one to ask as he's the CSS expert. Here's his latest word on Notes 5.5. The bottom line for me is that although we used to have to rely on editing our own notes.css which you'll find in the res(ources) folder in your Installation directory, just to compensate for Notes' quirkiness, not only is it not quite as necessary now that Notes is behaving better, it's becoming increasingly difficult to influence Notes via its CSS file in the latest version (see zenrain's post, also read his earlier ones on Notes). To prevent overwriting your custom notes.css file, and to tailor it to each Brain, put a copy in each Brain's _brain folder. PB stores its Notes material for any given Thought in a subfolder of that Thought's folder, in a folder with the reserved name of PersonalBrain Notes. Normally this file is empty except for images, as the real HTML is stored encoded in binary in a lob.db (Large OBject.db) file. You can force it to produce a simple HTML file named PersonalBrain Notes.html, by creating a virtual folder to an external folder on your hard drive, scribbling something into Notes, then examining the contents of your hard drive folder, where you will find this extra file. That's where the trail ends. This file looks innocent enough, but it states that it is designed to be rendered by the EditLive! module, so all the smoke and mirrors is in the way it's rendered, not the CSS you give it. If it doesn't like your CSS (and it won't), it will steam ahead and render it its own way, so unless zenrain can come up with more ideas, I'm afraid you're at its mercy. If (in HTML view) you simply paste in html created in another editor and don't disturb Notes by doing any editing in it, chances are that EditLive! won't change anything, so you can do it this way, but it gets pretty tedious after a while. This doesn't bother me personally much since I long ago gave up using Notes to do anything fancy and simply want it to perform faithfully as a plain text editor, with the minimum of extra formatting. If you want anything more than this, you should consider adding an HTML file as a file attachment, rather than use Notes. Please correct me if I've committed any gaffes here. By the way, don't waste time trying to search for "CSS" in this forum. The search engine here is so crummy that it won't search on three letter words such as CSS, tag, log and all the other useful terms (even color), nor has it learned how to search on phrases. You're better off using Google for this purpose.
PB 18.104.22.168 on Windows XP, J-1.6.0_17