Minimalist theme: Card Detail panel border

Hello!
I'm trying to get rid of (or subduing) most of the elements of the Forge theme for a calmer look, but I just have to ask: is there any way for me to alter the Card Detail panel border (white box on the left in my "theme")? Maybe in the code itself? Would like to set it to a single subdued colour, where it doesn't change according to the card hovered over.
In any case, of course, already really happy with the customisation options as they are. And with the program itself!
Salut!
I'm trying to get rid of (or subduing) most of the elements of the Forge theme for a calmer look, but I just have to ask: is there any way for me to alter the Card Detail panel border (white box on the left in my "theme")? Maybe in the code itself? Would like to set it to a single subdued colour, where it doesn't change according to the card hovered over.
In any case, of course, already really happy with the customisation options as they are. And with the program itself!

Salut!