Adding a fixed class to a div on scroll

I want to give the sidebar_wrapper a position of fixed when the page scrolls to its (sidebar) bottom content while the left-side continues to scroll independently because the left-side has more content than the sidebar div. I am using Tailwindcss.

I am struggling to make the code work.

The code has two issue

1. when the scroll starts, the sidebar_wrapper div overflows the sidebar and does not add the fixed class to it then it reaches the end of the sidebar content.
2. when scrolling back down, the sidebar_wrapper div remains fixed on the top position.

I want it to reverse the operation.

here is the code

<div class="grid grid-cols-1 md:grid-cols-[2fr_1fr] ">

   <div class="left-side">
     content .....
   <div>

    <div class="sidebar>

    <div="class="sidebar_wrapper">
       content....
     </div>

    </div>

 </div>

<script>
    let sidebar = document.getElementsByClassName("sidebar")[0];
            let sidebar_wrapper= document.getElementsByClassName("sidebar_wrapper")[0];

            window.onscroll = () => {
            let scrollTop = window.scrollY;
            let viewportHeight = window.innerHeight;
            let sidebarTop = sidebar.getBoundingClientRect().top + window.pageYOffset;
            let contentHeight = sidebar_wrapper.getBoundingClientRect().height;

            if( scrollTop >= contentHeight - viewportHeight + sidebarTop) {
            sidebar_wrapper.style.transform = `translateY(-${(contentHeight - viewportHeight + sidebarTop)}px)`;
            sidebar_wrapper.style.position = "fixed";
            }
            else {
            sidebar_wrapperstyle.transform = "";
            sidebar_wrapperstyle.position = "";
            }
            };
</script>