CSS - Set Div Width 100% and Resize Keeping Aspect Ratio

Question

I have a div with a background image that will overlay part of the header slideshow. I want the width of the div to always be 100% of the window size, even when the user re-size

Answer 1

This is what I've used in the past to support back to IE8. Used in conjunction with a small js plugin here that supports the filters: http://louisremi.github.io/jquery.backgroundSize.js/demo/

img {
-webkit-background-size:cover;
-moz-background-size:cover;
background-size:cover;
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='cover');
-ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='cover')";}
background-position:50% 0;
}