Fix: Skip Nav - Remove skip nav page jank

[machikoyasuda]

closes #1661

This was bothering me a lot 😓 and I finally looked up a solid, easy solution w/o any drawbacks. Currently, when using the Skip Nav to get to #main-content and then continuing to use the keyboard for navigation, the site will scroll you back up the page when you go from #main-content to Previous Page. It creates a jarring user experience, where the page goes down, and then back up. This PR fixes it by adding a scroll-padding-top that's greater than the height of the nav (80px), so the screen doesn't move back up. This solution also doesn't affect anything else (like the footer position, main container height, etc).

Before	After

• Uses scroll-padding-top from this: https://css-tricks.com/fixed-headers-on-page-links-and-overlapping-content-oh-my/
• Note: You have to test it with the DEBUG bar hidden. Doesn't work with the DEBUG bar on.