animate mode button size

Hi its strange that animate mode switch button is smaller than other buttons on canvas window. Looked at src , if use NORMOL_BUTTON instead of SMALL_BUTTON, the side is ok but there is button border appears, so this is not the right way for it. Does anyone help? thanks.

It also changes from theme to theme. I think that the only way to make it better is to use a custom button like the lock keyframes one.

It seems like it is a task that I can do, added to my TODO :mrgreen: