How to use CSS in system?

In general, there should be only ONE main CSS for one whole system. Likes in Drupal, it uses the theme's CSS, basically call it style.css in standard. However, some Drupal plugins or modules have their own CSS, but they named it accordingly to the module's name or folder. E.g., there's own CSS in forum folder or module, so they'll name it forum.css and put it inside forum module folder.

For our standard also, we should strictly follow this consortium. In the sense that let's say we have "people" system, so there should be people.css or style.css in root or include directory. If then we have male and female modules uses its own CSS, we'll call it male.css and place it into male directory, and female.css inside female directory.