[TASK] dropdown menu will go to navigation bar when scrolling the page.

[bingzhang]

https://user-images.githubusercontent.com/22112888/216093907-fe9473f7-1644-4925-aab9-affcb640aa95.png

the built-in dropdown menu can also go to the navigation bar. Just when you scroll up/down when the dropdown menu is expanded, you can not scroll up/down the whole window.
In our current code, we scroll up/down the whole window.

Those are the tech ideas how we disable/enable scrolling the window.

disable scrolling on the page
refer to the code: https://www.geeksforgeeks.org/how-to-disable-scrolling-temporarily-using-javascript/

enable the scrolling on the dropdown menu. (@sandeep-ps we need GUI designer for the scrolling on the dropdown menu)