Indent subnav items on mobile

[hupf]

Given the following example: https://puzzle.github.io/puzzle-shell/?path=/story/puzzle-shell-examples-web-app-with-navigation--default

On desktop the nav items look like this:

On mobile the nav items look like this:

The sub nav items ("My Time Tracking" and "Reporting") should be displayed indented, similar to the "Account Settings" and "Logout" dropdown items in the following screenshot: