With MUI 5.0.2, When all the IconButton-s in a ButtonGroup go on the same side, the hover background shape will change.
And other elements also affects this (a Button with/without href property on one side)
It is said in another question by @Ryan Cogswell, that the styling for the border is using :not(:last-of-type) in the selector. This implies that MUI is using class on and , which seemes very slopy to me.
Is this is a bug?
I hosted a minimal environment with GitHub Pages. The question is shown on the first and forth chapter.
(all pictures shown here are showing with on hover)
Button with href
Button without href
Button without href on hover
Also I made a related issue on official repo, and in my Learning note