[Plugin: Lightbox Gallery] Delete yellow frame around image in the article

Hi there,
just installed the lightbox, all working fine but i want to get rid of the yellow frame around the selected image/thumbnail. where can i modifie the code, i cannot find the right line and what shall i delete/replace?

thans much
Tronic

exsample page on my website

https://www.ads-software.com/extend/plugins/lightbox-gallery/