I want to apply a transparency or opacity to a div layer on my site with a light purple fore ground that you can see the black background through at a certain percentage. How would I write the code to do that?

My brother used this code for a css site that he did but it's not working for my div layer.

MOZ-OPACITY: 0.75;
OPACITY: 0.75;
FILTER: alpha(opacity=75);

Any help would be greatly appreciated. Thank you!!!

The first line should be -MOZ-OPACITY: 0.75;
If it still doesn't work after that adjustment, please post the whole code you're using or a link to the page.