Finding a color line in QSS

[Primus]

Hi. New to this forum, I've been using XnViewMp for years (Linux Mint) without any problems but I'm having a problem with the interface colors. I have activated the dark theme and I would like to know how to change colors #2 (25, 25, 25) to have color #1 (54, 54, 54).

copie.png

I've tried in the style sheet but can't get anywhere.

Thanks in advance.