You don't need to imagine. You can do this today with one line of CSS and another of JS. Custom elements are part of HTML5: https://html.spec.whatwg.org/multip

You don't need to imagine. You can do this today with one line of CSS and another of JS. Custom elements are part of HTML5: https://html.spec.whatwg.org/multipage/custom-elements.html#custom-elements-api https://html.spec.whatwg.org/multipage/custom-elements.html#... And you can override the "display" property with CSS.