Children items in menu can be pushed offscreen

[davidakennedy]

Creating ticket from 38623 from WordPress.org user ashercantrell:

Received a report today that the menu in Twenty Sixteen was causing child items to appear off the left side of the user's screen, making them unreadable.

It took a few minutes to replicate, but I found the issue. Typically, the theme's menu is on the right-hand side in a desktop sized browser window and is on the left on mobile, but just in-between desktop size and mobile size, the regular desktop menu just moved to the left before it's turned into a mobile menu. So on certain resolutions (or if you manually resize your browser window like me), this happens:

See: https://cldup.com/W9WGKB02jF.thumb.png

User's site is namcoa.com. I was able to replicate with a test site:

See: https://cldup.com/oSItVP0Oki.thumb.png

This appears to be a specific case where:

1. A user has Twenty Sixteen
2. Has a menu item with sub items (or sub sub items) in the first slot
3. Is using a display at just the right (or wrong?) resolution where the menu hasn't quite turned into its mobile form
4. I had trouble replicating on my own at first, but it seems that your site needs to have a sufficiently long title, also.