Forms without CS File?

Question

I have seen a project , when i open it as a site then
there is a website "easyjobs" and one asp.net webapplication "job_Catalog".
both have same forms but in easyjobs there is no cs file.
when i click on any button then job_Catalog will be called. (because it is inherited ) ,
I unable to understand this concept why we need to put this forms in tow place one with cs and one without cs.
can any body tell what is this?