Google-chrome – Grab favicon.ico using Google Chrome dev tools

(Update 2014) Since support of user stylesheets was recently removed from Google Chrome, the only option for this moment is to use extensions (like Stylus *1), but these will behave differently (see below).

The most relevant request for re-introducing true user stylesheets in Google Chrome is Issue 347016: Support user stylesheets.

Per specification, "true user stylesheet" rule has lower origin specificity in cascade than author rule, but !important user stylesheet rules have higher origin specificity than !important author rule, regardless of its selector specificity.

Extensions mimicking user style-sheets in Chrome simply injects (hopefully) last style element into page, what have some consequences:

• such style is at "author level" in the cascade, so you must make sure your !important rule has higher specificity than one you want to override
• "your" injected style is exposed to page scripts, so they can easily delete it at will.

*1 Original extension, Stylish, is currently (2017) in state of erratic development by a new mainetainer, so I'd advise to avoid it and use alternative like aforementioned Stylus.

(Following original answer is now obsolete.)

Afaik it is not possible to tweak the UA css itself, but you can make a global userstyle: start Chrome once with --enable-user-stylesheet. This will create <user-data-dir>/<profile>/User StyleSheet/Custom.css which you can use (changes are propagated immediately). http://code.google.com/p/chromium/issues/detail?id=2393

To fix this, I went into Preferences, Under the Hood, Clear Browsing Data, and selected all the options with "from the beginning of time" as the date reference. I was hoping to not have to do this and lose all my browsing history/data, but it worked.