"Back to top" navigation on long pages

[klohman]

As a SmartPay website user, I need to be able to navigate quickly back to the top of the page, so that I can easily access features on the global header.

AC:

• [ ] Add "Back to Top" button that scrolls page back to the header
• [ ] "Back to Top" button displays only when user has scrolled [need to determine length] from top of page
• [ ] "Back to Top" button displays on all pages when scroll minimum has been reached

Notes

Example implementations on USWDS sites:

• https://tech.gsa.gov/playbooks/database/
• https://www.va.gov/health-care/about-va-health-benefits/
• https://www.epa.gov/bedbugs#top
• https://tech.gsa.gov/
• https://department.va.gov/

[klohman]

@rebekahperillo @JessicaMarine1 We should review this one at next grooming.

[JessicaMarine1]

7.19.2023 - Decided this was a post-MVP "nice-to-have".