modal-focus-trap.js VanillaJS library for trapping focus within an opened Modal, and returning focus back to the element triggering Modal. References Dialog (Modal) Pattern (www.w3.org) Modals (Dialog Windows) (web-accessibility.carnegiemuseums.org) Best Practices for Modal Windows (uxmovement.com) Where should keyboard focus go in modals? (accessibleweb.com) Restoring ActiveElement Focus After A User-Interaction In JavaScript (www.bennadel.com)