For some reason this does not work anymore. The I.D. on the Eurasian Chess page also lost its background, and I am sure this worked before. Is there some global style definition now that gives
elements a background color?
Looking at it with Web Developer Tools in Firefox, I see that TABLE TR has the background-color value of var(--nav-bgcolor), and when I turn it off, the background image shows up. With that in mind, I added this to the Eurasian Chess page, and that fixed it: