How do new browser windows cache files?

My situation:

I have a website example.com and from this website I'm launching new windows of the url test.example.com?variousGetStuff and I'm caching files loaded within the new window. My question is, after the files have been cached locally, if I then close the window and open a, second, new window under test.example.com?otherGetStuff , will the cached CSS files persist?

Furthermore, if they do persist then if the second new window has different CSS to the first new window then will these cached CSS files conflict? (Assuming the same file name).