opop, it is a non-essential part of a forum setup, the team did not see it necessary to implement when the system was first developed. There are advanced means of creating sub forums however the standard system will not provide these as Sunny has already stated.
As to th design these forums and all existing official uCoz support forums currently have unique designs limited to the use of the official team. They are not provided as part of the standard system nor are they available to our users for use.
Jack of all trades in development, design, strategy.
Working as a Support Engineer.
Been here for 12 years and counting.