Navigation button over function with 2 images

Hi I'm creating a navigation bar with previous, pause, play and next. I wantr to have a hover imgae like a rollover effect like in most HTML editor. 

I use the change state with my 2 images (see attached) one for actual previous and the one when the mouse is over.

In the trigger I choose for the hover image : Hidden when the timeline beggin and Normal when the mouse is over. The hover image is on the top of the actual previous image. 

Should this work ? Is there another way to do this ? I try with Storyline forms and its work directly in the states I change (hover, normal).