Hi Dustin,
Thanks so much for your report!
Scenario 1: The margin-left is added to the button but not to the li, which is added automatically. If you wrap the button with a li (div set to li) and give it margin-left: auto, it works fine (which is to be expected).
Scenario 2: if you look at the builder source code, you will see that the button on the canvas is not wrapped with a li. menu item, so your CSS cannot work. Presumably, the code currently only provides this for text links or dropdowns. I’ll create a task for this.
Best regards,
timmse