#header h1 a{
display:block; /* Required */
width:250px; /* Width of image in question */
height:70px; /* Height of image in question */
position:relative; /* Required */
}
#header h1 a span{
position:absolute; /* Required */
width:100%; /* Stretch full width of parent */
height:100%; /* Stretch full height of parent */
background:url(images/logo.gif) top left no-repeat; /* Image */
cursor:pointer; /* Required for links to appear like links in IE */
}
<!-- THE HTML -->
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