That code is scss are you putting it an scss stylesheet or a normal one?
If you are trying to put the code in a normal stylesheet then you need the compiled version which you can grab from codepen (click view compiled in the css window). I assumed you had written that code and would know how to manage it
Yes I’m not a big fan of bootstrap either but I believe the hamburger icon button should have a sr-only element (screen reader only) added to aid navigation and aria attributes as per the default in bootstrap.
I’m less and less a fan of “screen reader user” code.
I’m way more happy with your “add the word Menu” option. Cause “screen reader code” doesn’t help a Dragon user click that button, esp if the X is made of an icon-font (quite popular in Bootstrap).
It also helps users like my wife who have no idea what that hamburger button is supposed to do (and she’s on her phone all day but hasn’t grasped what the icon is for)