WordPress’s Elementor’s Nav Menu when set to “Dropdown”, was opening “inline” and moving subsequent header content down the page, rather than opening in a separate layer over the top of my header. The solution……was to make the Nav Menu’s position “Absolute”. In its Advanced menu, in the section “Positioning”, simply change the “Position” setting from “Default” to “Absolute”. I don’t think this changes the CSS z-index, only changes how the Navigation Menu is displayed.