Help me with some elements for darkmode?

Hi, cuz my site have darkmode option, i’m adding .darkmode elements in my style.php from the wpforo. Right now i’m to change the color of few elements, but i cannot find the right code.

Check picture – https://prnt.sc/KxMP4EkcLsu3

Can u tell me from where to change that White color? Or maybe that’s like mini-image? I want to change it to black or transperant.

The page I need help with: [log in to see the link]