How to keep image width the same as window size

[dremarile]

i am using an image slider for a website and need the image to stay the same size as the window depending on the width of the window.i have this in CSS:\[code\]#slider { width:100%; height:306px; background:#fff url(loading.gif) no-repeat 50% 50%; position:relative; margin:0 auto; box-shadow: 0px 1px 5px #999999;#slider img { width:100%; height:306px; position:absolute; border:none; display:none;}\[/code\]and the HTML:\[code\]<div id="slider"> <img src="http://stackoverflow.com/questions/15794630/images/image-slider-2.jpg" alt="" /></div>\[/code\]so the #slider is the div id and then #slider img for the image but its not keeping the image as 100%any ideas on this?Thanks