Your advice to add this in appearance>theme options>layout settings>Custom CSS box:
ul#thumb-list li img, ul#thumb-list li{width:auto;}
didn’t solve the problem with the width of the thumb-tray. It just changed the width of the thumbs themself and extended the empty space between the last thumb and the end of the slider.
I added
#thumb-tray{ position:fixed; z-index:3; bottom:0; left:0; height:130px; width:93%; overflow:hidden; text-align:center; margin-left:4%; text-align:center;}
as well to appearance>theme options>layout settings>Custom CSS box
which almost solved my request but it extended the empty space between the last thumb and the end of the slider even more.
Any ideas how to suppress the gap at the end?
Thanks!