Adjust vertical padding and border width for navbar-nav links (#42158)

* Adjust vertical padding and border width for nav links

Adjust vertical padding and border width for nav links

* Update scss/_navbar.scss

Co-authored-by: Mark Otto <markdotto@gmail.com>

* Comment out nav-link-border-color variable

Added support for an optional border-color

* Typo

Used , instead of ;

* Linter

* Reorder for consistency of states

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Co-authored-by: Mark Otto <markdotto@gmail.com>