So I am exploring subtheming. and because i am a bit OCD, i have to understand the whole underlying thing. so i have been looking at the core files; not to hack but to see what the overrides and intercepts are actually affecting. Here are the core CSS files in Drupal 7
then, if you enable the stark theme, you will see a little bit more styling. stark contains:
if you remove the reference to the css file for stark in the .info file you will see what the default css styling looks like. this helped me to see, literally, the consequence of the styling in layout.css. and since i am a monkey, i need to see it… and because i am an idiot.