CSS issue due to element-style

Hello opajaap,
I need your help for the personnalization of my galery.

Here are two screenshots of what I have to do:
https://www.kalidao.com/screenshot/portfolio-liste.jpg
https://www.kalidao.com/screenshot/portfolio-detail.jpg

My bigger issue is with the element-style. For exemple I want to personnalize the border of the image thumbnail but I can’t because of the element-style set to border-width: 0;.

Same issue with the detail view. I want to move the previous and next button outside, on each side of the image.
But I can’t because “bbb-l” element-style is set to:
position: absolute;
left: 0;
top: 0;

I also want to align the description text of the detail view in left but I can’t do that with CSS: imagedesc-1 element-style is set to text-align: center;

Do you have a way to disable element-style for some elements of my galery? Or any other solution to build my mockup with CSS?

Many thanks by advance.