Hi,
I would recommend you to first use the native XR support and not use the VR experience helper with XR (as it will not be further developed).
I just noticed that the div container of the button has no css class you can manipulate. I will add one (please create a github issue if you can). If you use javascript, you can find and manipulate the parent of .babylonVRicon in the meantime.
Regarding collisions, you can see this discussion - (WebXR) How do I add collision detection to the webXR camera?