Multiple Background Images?

Hello,

I’m using Duena theme. I am attempting to have a background image with a raster pattern image overlaying it. Like this site for example. You will notice that it has the large greenish image in the background with a pattern overlaying it.

I found the section in my stylesheet for the background. I’m guessing I just need to edit this code somehow but nothing I’ve tried has worked.

All help is much appreciated.

body {
  background-image: url(images/main-bg.jpg);
  background-repeat: no-repeat;
  background-position: center 0;

}