As explained to me in previous posts, in order to change a specific area of a page with CSS, one should “target” that area by identifying it with its identifier.
Wanting to change the background on the large image display when below 800px, I wrote some CSS based on the identifier found in the body section of the source code.
On the source code page, the identifier is: album-template-identifier-artwork it seems to me.
But my CSS does nothing…