Map hover background color

I have a very simple HTML map that is divided into 9 sections ( Selecting any section then loads a pdf file with a larger view of the selected section. What I would like is for the area under the hover to appear with an opaque shade to thus indicate the area.

I have tried the following, but it does not work.

map > area:hover {
	background-color: gray;
	opacity: 0.2;
	border: 0;

TIA for any help.

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