how to add costum banner

this is the code im using but its not working is it right?

#logo h1 a{
background:url(https://img836.imageshack.us/img836/7/160155383b58335m3.jpg) no-repeat top center;
display:block;
text-indent:-9000px;
width: xxpx;
height: xxpx;
}

and im in the style CSS under the header section is that where it goes?