Thank you! :) If you go to a site like colorpicker.com, you can type in the hex code you want to use (or use the palette that's right there to find the code) -- off to the right you'll see three boxes for R, G, and B.
In the coding, you'll see color:rgba(xx,xx,xx,xx) with the xx's being the R value, then the G, then the B -- just input those values in place of the ones that are already there. The last value, A, is an opacity value. If you like it how it is, you can leave it alone, but if you want to change it, it's on a scale from 0 (transparent) to 1 (opaque) -- so 0.5 is half transparent, 0.8 is a little less transparent, etc.