how can i change the background color of the imagegallery-thumbnailsarea ?

i have allready analysed the style under google.developers and found the style in rigThumbnailslst, but if i change the value in skins/imagegallery.css nothing is taken and nothing happens.

Add functionality that will pause the timer for displaying the next image (e. g. on mouseover).

The timer should resume when the mouse leaves the image area.