Difficulty changing header image in PHP/CSS

Hi,

I am trying to change the header image for a specific page in the Twenty Twelve template.

Seen here: http://www.robotspacebrain.com/keyz/

I can’t seem to get the image to show up…

My style.css:

#header-keyz {
  background: url("<?php bloginfo('stylesheet_directory'); ?>/images/Keyz-1200.jpg")
  no-repeat bottom center; }
#headerimg-keyz  {
  margin: 0px 0px 0;
  height: 194px;
  width: 1200px; }

And my header.php:

<div id="header-keyz">
 <div id="headerimg-keyz">
   <h1>
    <a href="<?php echo get_option('home'); ?>">
       <?php bloginfo('name'); ?></a>
   </h1>
  </div>
</div>

I’m trying to implement the information found from the designing headers section on WordPress