2 Refactor JS and CSS to top- and bottom- sticky element to reduce scroll jank

I have a menu that is made both top- and bottom-sticky by Javascript. (demo visible at [login to view URL] ) (It also scales continuously via Javascript, and changes layout by CSS, in response to screen size and orientation.) But the scrolling is not quite smooth at the start and end of stickiness, and it shows too much scroll jank when implemented. So I would like the code refactored to scroll more smoothly and retain the other functionality. Rather than optimizing the existing Javascript, I would like a new method using some advanced CSS technique, or Waypoints, plus maybe a workaround for iOS browsers like Scroll Snap. In your bid message, please indicate what technologies you would try. Also, could you please suggest how I should assess your level of effort and success on this project. For example, will you use the time tracking app, offer a performance guarantee of some sort (perhaps measured by the tool at [login to view URL] ), a list of code improvements, or something else? This contract will include installation of the revised and new code on my web site at [login to view URL] , where the current menu is temporarily functioning. If there are other ways you would like to propose to improve scrolling on the main page there, I would like to hear about that too! Thank you.