title: Translucent nav bar with background image behind: css, no javascript
body: <p>Bit of a newbie, but trying to do something i thought would be quite simple; i'd like a full screen background image with no margins, that scales to screen size (i'm using background: cover; at the moment) but I'd like to put a translucent nav bar over the top of the image right at the top, containing a horizontal menu.</p>
  
  <p>So far, I have the nav bar, but the image is sitting either above the nav bar, or underneath it, instead of directly on top. What's the best way of doing this, is it z-index values, or is there something easy i should be doing to place one div (.nav) over another (.background-img)?</p>
  
  <p>any help much appreciated, sorry if this is a bit vague but i am a total newcomer to html &amp; css!!</p>