Wordpress Twenty Twelve Full-screen Responsive Background Image

Question

I have just started front-end development with Wordpress Twenty Twelve child theme.

I want to make my background full-screen responsive. I followed from this post: Full-screen responsive background image because it is exactly what I'm looking for.

But when I copy and paste this css code into my style.css:

img.bg {
  /* Set rules to fill background */
  min-height: 100%;
  min-width: 1024px;

  /* Set up proportionate scaling */
  width: 100%;
  height: auto;

  /* Set up positioning */
  position: fixed;
  top: 0;
  left: 0;
}

@media screen and (max-width: 1024px) { /* Specific to this particular image */
  img.bg {
    left: 50%;
    margin-left: -512px;   /* 50% */
  }
}

It doesn't work. It feels like img.bg doesn't exist. This is my current website .

Please help! I cannot move on without this and I'm behind schedule :( Thank you for your time!

Answer 1

You need 2 use the jscript instd. As exmpl:

        var theWindow        = jQuery(window),
            jQuerybg              = jQuery("#bg"),
            aspectRatio      = jQuerybg.width() / jQuerybg.height();
        function resizeBg() {           
            if ( (theWindow.width() / theWindow.height()) < aspectRatio ) {
                jQuerybg
                    .removeClass()
                    .addClass('bgheight');              
            } else {
                jQuerybg
                    .removeClass()
                    .addClass('bgwidth');               
            }

        }

        theWindow.resize(function() {
            resizeBg();
        }).trigger("resize");

Answer 2

There's a nice css way of doing this:

div
{
position: absolute; width: 100%; height: 100%;
background-image:url('smiley.gif');
background-repeat:no-repeat;
background-size:cover;
}

The key is the background-size: cover; line - it will resize no matter what the window size. Check it out at http://www.w3schools.com/cssref/playit.asp?filename=playcss_background-size&preval=cover