[Typo3] tt_news and css

[mario]

hello, 
I know I should know, but I am unable to get at it. 

I am trying to use tt_news. Under /static, I see four subfolders (typo
3.8.0), hence four setup.txt files. I understand they are four different
options (are they?)

In general, how do I select one of them?

In particular, I see plugin.tt_news .. _CSS_DEFAULT_STYLE twice (within
static/css/ and static/ts_old). 

By deafult, typo3 seems to use the latter. How do I force it to use the
former? 

More in general, if a hacking an extension, what do I need to care about
if I want to get the setup within the static/setup.txt file into the
<style> portion of the final html output?

It is great if you might tutor me, or point your finger to the useful
piece of documentation.

my best
mario