For the combobox, checkbox and slider you don't have a On Hovered event or On Pressed event which could come in handy to some people if not a lot and the sliders doesn't have an image for hovered and pressed either. I know the combobox and checkbox both already have a hovered and pressed image but no events and the slider doesn't have either

This could be beneficial to some people as it would allow people to see what they have clicked if using a controller or even just a keyboard, (not mouse) as it is kind of difficult to see whats being hovered over when using said controller and for the slider it could be a pressed event to help indicate when selected and can be moved on whatever axis.

In short:

On Hovered and On Pressed for the above UI and Hovered and Pressed images for the slider.