Invert burger menu color on scroll

Using code I found from @tuanphan, I got the logo to change color on a fixed, scroll-back header. Does anyone know how to change the color of the mobile burger menu on scroll? I have the mobile menu activated for desktop. 

https://helicon-oval-8wh9.squarespace.com/

PW: admin

You mean burger icon? You can use this code to Website > Website Tools > Custom CSS

header#header.shrink div.burger-inner>div {
    background-color: #f1f !important;
}