What is the best way to set frame with app to have full screen height? I found “ACE” app could handle it with data-options attribute "sizeToParent:true in the script tag, has any idea fix it in forge app
Hi @oh4mm ! Welcome to the developers community ! 
That depends on what type of application you are trying to create. Here are the documentation for the UI interface:
https://developer.atlassian.com/platform/forge/user-interface/
In short UI kit is a set of ready to use components where Custom UI will give you freedom of writing your own styles (like setting height for frame).
Best regards,
Jaroslaw