Fix navbar height problem in fruitsalad theme

The navbar is missing some vertical spacing, which turns out to be because the line-height defined for the global li selector overrode the line-height for #submenu Fix this by also adding the rule under #submenu li.
Revert "Fix navbar height problem in fruitsalad theme"

This reverts commit 7d503912cddb40d6d144b64ef1c0212652088995.
Add line-height attribute to fruitsalad main.less
Merge branch 'main' into mit-theme-tweaks
Merge pull request #959 from learning-unlimited/mit-theme-tweaks

Fix navbar height problem in fruitsalad theme