I developed a theme for WordPress with a simple registered menu. My HTML / CSS theme has two types of dropdown menus (closely, that is a level and wide, these are two depth levels).
Now I want to add one Select a box Under My menu options in the WordPress menu area, select one of the drop-down types for the menu entry and then add the associated class to the sub-ul in the HTML code.
I am not a professional WordPress and PHP developer and have a little experience with theme development in WordPress and registering menus in functions.php. Please provide your answer with full details and file names, which I have to give you as an example code.