There are no such limitations for Trial versions. The issue could be related to wrongly cached simulator files. To check this, please navigate to the %localappdata%\Telerik\BlackDragon\Cache folder
and delete all of its content. Note that, all AppBuilder clients must be turned off before that. After you have deleted the cache, please check if the simulator will show you the CSS.
Also, I must note that with the yesterdays AppBuilder 2.5 release we introduced a critical bug within the simulator that prevents the correct rendering of CSS transitions. The good news however is, we have scheduled a hotfix for this for the upcoming week.
I hope this helps.