Change dropdown color por projects

[Diagonal]

Hi there!
I'd like to change the background color for the dropdown menu (mobile) in every project. Projects would be white, instead of the green background used for pages.
Here's the code I am currently using, but it's no working:
nav.primary[data-type="project"] .sub-menu { background-color: #FFFFFF; }
Sorry I have no idea about coding, but I usually find the solution in other forum topics... Thanks so much for your work here!

[mariusjopen]

Dear @Diagonal

try this with CUSTOM CSS:

.id-199 .menu-item a {
    background: red !important;
}

Your current page ID needs to be there instead of 199.

All the best!

Marius