Create code that will allow me to show different banners based on screen size.

I am looking to show a different ad code based on the end user screen size. I would like to use css and div to make it work. I have played around with this but cannot make it work: media all and (min-width: 959px) { .content .x700{display:block;} .content .x490{display:none;} .content .x290{display:none;} } @media all and (min-width: 720px) { .content .x700{display:none;} .content .x490{display:block;} .content .x290{display:none;} } @media all and (min-width: 479px) { .content .x700{display:none;} .content .x490{display:none;} .content .x290{display:block;} } Script (google adsense and other ad code) will be placed between the <div class="xxx"> </div>. You must be able to speak English. You must not ask for milestone releases before it works 100% on our site. You can set up an example on a test site on your server, and then I will add it to my server for the final test.