Hi, @avisor. Glad you caught me just before logging out.

Yes, the tabs/cards are there to tell you the themes of the ongoing contests(and ended ones).

As for the number of entries allowed, I actually asked @tasteem the same question! They told me that you can post as many times as you want, in one contest or more, except that the upvotes they promise to all the participants will be limited to 12 times a day. So you can post 12 times a day and get upvoted every time for participation. (Of course, the posts would have to be of decent quality, as to avoid being blacklisted or something!)

Hope this helps!