Change background color of widgets / notifications in layan solid

[afland]

I really like this theme overall but I'd like to make the background color of widgets like application menu and calender to be a little darker.
I tried editing some of the svg files in the desktoptheme folder after installing Layan-kde, but I couldn't get any colors to change. I have no idea how svgs really work, so I just used the paint bucket tool in inkscape to try and change the colors in background.svg for example.
Specifically, I want to change the widget / notification color to be exactly like or just a little bit ligher than the background of dolphin.
Any help would be appreciated