[html] How do you make a div follow as you scroll?

The post is old but I found a perfect CSS for the purpose and I want to share it.

A sticky element toggles between relative and fixed, depending on the scroll position. It is positioned relative until a given offset position is met in the viewport - then it "sticks" in place (like position:fixed).

    div.sticky {
        position: -webkit-sticky; /* Safari */
        position: sticky;
        top: 0;
        background-color: green;
        border: 2px solid #4CAF50;
    }

Source: https://www.w3schools.com/css/css_positioning.asp