Hamburger background fade

Hi,

I have a background that applies to the hamburger menu when the X appears. How can I get that background to fade in/out?

Thank you!

https://www.pacpeaceproject.org/bios


Here is my site Read-Only: LINK
(how to share your site Read-Only link)

I’m actually looking to do something like Starbucks does on their hamburger menu where the hover on both open and close has a background color that gowns in and out: https://www.starbucks.com/

No one? I have tried for days any tips would be greatly appreciated thank you!