I saw that someone requested this a long time ago, but it would be nice. Not essential, but nice. Maybe just for text buttons?
I’m pretty sure you can set that individually in your browser. At least in Safari you can store a stylesheet.
@Chaya, Yep that was me!
I’m keeping my fingers crossed it will be here soon!
To get around it for now I drop a bit of CSS into the Sparkle project -