Thanks so much for your help, I really appreciate it. Now I know why my code never worked, I forgot about the nth-child part.
Here's the full code with the Back button alignment fix for anyone else who needs it...
.header-menu-nav-folder-content span:nth-child(2) {
margin-left: 25px;
}
.header--menu-open .header-menu-controls-control--active {
margin-right: 55px;
}