floating, sticky, transparent, left menu

Hi, I saw this awesome side-menu at https://int.stinegoya.com

  1. It sticks while scrolling
  2. It floats over the content, which is funny
  3. In fact no 1. because the most important: The dropdownmenu stays open while one search in the specific categorie, also in the mobile version. If the visitor changes the categorie, that one stays open. That is important, because visitors then are just one click away from the category they were searching in. Most menus close, so the visitor needs 3 or 4 clicks to get back to their favorite category.

Does anyone know a theme or plugin that provides this?