You can use the css below but there is a catch
background-color: rgba(255, 0, 0, 0.5);
As Christopher mentioned different browsers render elements differently so the declaration above will work for IE9 and FF but Chrome will only make the dropdown section's background transparent. Also remember that the above will probably not work prior to IE9 so you may need to use an image for that purpose in an IE-only stylesheet.
First, solve the problem. Then, write the code.
“Don’t worry if it doesn’t work right. If everything did, you’d be out of a job.” - Mosher’s Law of Software Engineering
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