Some fixes for reactbutton/extrabuttons

• Cleans up CSS for ReactButton and makes classnames more consistent with rest of buttons.
• Adds type="button" to popover's button to avoid form issues
• Fixes hitboxes of extrabuttons and reactbutton:
  
  Popover's button has 100% width that makes hitbox grow. Kind of a soft fix but maybe something more serious needs to be done for popovers, like not using button at all and let user of component declare button themselves?