Hello,
Please add this code in custom.css file
.mobile-nav,
.et-mobile-menu li > a,
.side-block .close-block{
background-color: #fff;
}
Here is a video tutorial how to create custom.css: https://www.youtube.com/watch?v=Qok2zRedRMY&feature=youtu.be.
Regards,
Robert Hall.