You would have to use css, I thought it would be something like position:fixed but just saw this: https://www.w3schools.com/howto/howto_css_sticky_element.asp
You call also just search for sticky div with css or sticky footer or sticky nav or to make it easier use this plugin:
https://ww.wp.xz.cn/plugins/sticky-menu-or-anything-on-scroll/
You will still have to know how to choose or name your selector but they explain it.
