I want to hide the menu from two pages

If you created the page, then it will probably have a page ID associated with it.

1. Do a view source on the page that you are interested in (Register/Login or Login page).
2. Look for the body tag. It will start with <body, so you can do a search on that string (a less than sign followed by the word body).
3. Once you find the body tag, you will see some class names inside that tag. One of the class names will look something like page-id-#, where # will be some number that will uniquely identify that page.
4. Do the same thing for the other page, so you have the page IDs for both pages.
5. The Interface theme has a custom CSS option, so from the admin dashboard, go to Appearance → Customize → Design Options → Custom CSS. You want to enter your new CSS rules here.
6. Let’s say that the page ID that you’ve discovered for your Login page is 7 (i.e., the class name is page-id-7) and the page ID for your Register/Login page is 13. So copy & paste this rule into the Custom CSS field:

   .page-id-7 #access,
   .page-id-13 #access {
      display: none;
   }

   Of course, replace the numbers with the IDs of your own pages. Click the Save & Publish button when done.

That’s it, the menus should be hidden on those two pages.