Divi Theme comes with a pre defined mobile menu button (hamburger button) in the Mobile Menu.
You can make a number of basic changes to the mobile menu in DIVI > THEME CUSTOMIZER > MOBILE STYLES
But there are a number of easy tweaks you can also make using CUSTOM CSS such as colour and size of the hamburger
Goto DIVI > THEME OPTIONS scroll down and in the section CUSTOM CSS add the required following codes.
To Change The Colour Of The Hamburger
(This example uses RED but you can use the HTML Colour Picker if you don’t already have one.)
To Change The Size Of The Hamburger