I kept looking and found the Menu and Inspect Element - it shows absolute position (clicking on the icon shows this is the menu element.  In any case, not resulting in a fixed position for the menu. Any suggestions?

I have the same question and I need a little more help.  When I go to customize>advanced>Custom JS & CSS, I get 2 windows - one for JS, and one for CSS. Do I enter this code snippet in both?   I tried in each one separately, and in both; did not have the desired result in any case.    Also, re your "check if you got the right element", I only have 1 menu.  When I right click that, I get a standard windows selection box, no "Inspect Element" selection.  Please advise.