Setting scrollbars for editor tab widget

I’m working with Editor Utility Widget. I’m using it as an an additional tab in editor. I’d like it to show scrollbars when the contents are bigger than current size of the tab. Since the user can resize the tab as they want I don’t have a fixed width and height.

I have my contents in two ScrollBoxes (one for vertical, one for horizontal). Since I don’t have a given width and height I don’t know how to set that…

You can get the widget size with GetAbsoluteSize, but you should call it in one of the mouse events, or any event that lets you access the UI geometry, like On Mouse Enter.