Adjust CSS for vertical navigation menu in sidebar and footer widgets

[bobbingwide]

The CSS that styles the main menu is also being applied to the menus in the sidebar and footer.
There are a couple of problems with this

1. It doesn't match what we see on the live site
2. In the sidebar the longer menu items get scrunched up.

[bobbingwide]

The menu styling change made in March relied on the navigation menu template part being given a tagName attribute of nav.

<!-- wp:template-part {"slug":"main-menu","theme":"sb","align":"wide","layout":{"contentSize":"80%","wideSize":"90%"},"tagName":"nav"} /-->

This tagName option is not available in the Site Editor. Is this an oversight?

[bobbingwide]

In the sidebar the longer menu items get scrunched up.

The longer menu items still get scrunched up in the main menu, especially when the mobile menu is being displayed. See #33

[bobbingwide]

The longer menu items still get scrunched up in the main menu, especially when the mobile menu is being displayed

Fixed by changes for #33 in v0.3.1. Closing therefore.