Glad you’ve found it helpful! I’ve been meaning to update that video. Here’s another approach that’s even easier -
Install and activate the Sagextras plugin by Michael Romero - https://github.com/storm2k/sagextras
add_theme_support('se-nav-walker'); to your functions, I usually drop this in the top of lib/setup.php, right below the Soil stuff.
Replace the contents of header.php with the contents of this gist - https://gist.github.com/johnny-bit/cc8840f148da01c2af52