Not an issue just showing as couple adjustments I made and letting you see them.

[freefreeno]

This is nothing more than letting you see these changes and then you can have a better understanding of what I am talking about.
This is the whisker menu after changing it to:

window#whiskermenu-window {
background-color: #333333;

Also I am using a different xfwm4 theme in this screenshot. It has that rolled back look that I really don't understand how is achieved but I love it. The xfwm4 is here.
https://github.com/B00merang-Project/macOS-Dark

I had to change the color of top thunar to match my xfwm4 but that is not something I wanted to do but I had to to use this xfwm4 theme.