To try out <selectmenu>, launch this page in Chromium (Edge/Chrome Canary) with the
command-line flag:
--enable-blink-features=HTMLSelectMenuElement
Countries can be added to the menu by typing them into the text box and hitting 'Enter'.
Countries can be removed from the list by clicking the 'x'.
Arbitrary styles can be applied to the <selectmenu>; note the use of images and try
applying some styles using the buttons.
In the source for this page, note that the page didn't need to include JavaScript to
open/close the select or to display the value in the button when an option is clicked, etc.