Pajamas site mobile nav

Purpose

As a followup to !3115 (merged) there are some additional improvements needed for the mobile navigation of the Pajamas website.

From !3115 (comment 1171724042):

…move from a partial cover to a full-width/overlay menu to:

1. Add a close button in correct focus order, potentially using a × icon
2. Remove overflow scroll of page content while menu is open (swipe moves content body not menu items)
3. Allow increase in touch targets in menu for mobile
4. Rethink ≡ overlapping page content on scroll