Body font implementation

Is our current system stack setting still the best approach?

See...
- https://css-tricks.com/snippets/css/system-font-stack/ 
- https://github.com/necolas/normalize.css/issues/665
- https://github.com/jonathantneal/system-font-css
- https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/