how can I link css file in activecollab in a custom module?

I am working on activecollab custom module, so have some problem in css file placement, i placed a file in

mymodule\assets\default\stylesheets\frontend\main.css

but after installing "mymodule", activecollab not fetching that css file on run time loaded page ..

if anyone did this please help me, is there need to add a line to link that css with module? or css folder issue?

UPDATED:

Additionally i want to know what is FRONTEND and BACKEND in assets/default/stylesheets/ folder of module?

is there i need to place my normal main.css file in frontend folder?

Solution

Frontend and Backend are contexts in which assets are used:

Frontend is public part of the application, that does not require login. It's used to serve shared pages, public request forms etc
Backend is everything behind login screen (basically, activeCollab's main interface)

My guess, based on your description, is that you are placing your stylesheets into a wrong context. Try backend, instead of frontend.