Adding extra css class for the .switch-button-background div

Hi Olance
I mainly add extra classname to the .switch-button-background div when state of the switch is changed.
I think it's a good idea to add this functionality. This would allow to change the css of the .switch-button-background from blue for on to grey for off or whatever different.
The extra two files is just an example from your page which also would be useful to add.

Best,
Milosz.