Hello,
I saw the screenshots you attached.
1) Please try adding the following Custom CSS in the Global Custom CSS area under Theme Settings >> Custom CSS.
.mfp-bg {
background-color: rgba(0,0,0,.7);
}
You can set the background color according to your needs.
2) Full screen option is not available for the mobile menu. Therefore you can change the position by editing the mobile header.
Screenshot for Clarification: https://gyazo.com/6dd2d96d436c7571a48a7ec5ccb342ea
3) To change the background overlay color try adding the following Custom CSS in the Global Custom CSS area under THeme Settings >> Custom CSS.
.wd-close-side {
background-color: rgba(0,0,0,.7);
}
For the background of the mobile menu try adding the following Custom CSS.
.wd-side-hidden.wd-opened {
background: red;
}
Regards.
Xtemos Studios