Regarding your patch, I see you remove all the "reset" in the CSS.
I'm not really sure we did that, but it's also not described and
explained in the commit log of your patch.
AFAIR, CSS reset is a means to equalize the default looks of the basic
elements between different browsers.
But was it just an arbitrary choice, or was there a particular reason
for it?
Not sure I understand the question. When you start from a CSS reset (which
creates a bare-bones look), you more or less test in one browser and know
how the website looks in others. Modulo engine bugs, of course.
Otherwise, to make the website look identical across browser, you have to
make sure to enumerate all disparities in your own styles.