I am working on a page in 7.1. They wanted a burger-style nav for their desktop site, so I added the below code and successfully achieved this. I would like to know how to best add a background image (custom files)? Alternatively, how to change the background colour and the width of the open navigation (in particular when on desktop). Plenty of thanks in advance!
.header-burger { display:flex!important}
.header--menu-open .header-menu {opacity: 1!important;visibility: visible!important;}
.header-nav, .header-actions {visibility:hidden!important})