rl-
The css you're adding should go in your child theme's style.css anywhere under the last @import
Are you trying to replace the blog-title "Ecotourism" text with an image? If so you'd need apply your css to #branding not #header. Text indenting #header will shift your navigation off the page. Also using a text indent of -9000px could lead to accessability issues if the image doesn't load.
I prefer doing this with Thierry Image Placement. Follow the link for the full descrpition.
With thematic you'd have to first pull the blog title text out of the anchor. In your child theme's functions.php put:
function remove_thematic_header_actions(){
remove_action('thematic_header','thematic_blogtitle',3);
}
add_action('init','remove_thematic_header_actions');
function tip_child_blogtitle() { ?>
<div id="blog-title">
<span>
<a href="<?php thm_bloginfo('url', TRUE) ?>/" title="<?php thm_bloginfo('name', TRUE) ?>" rel="home"></a>
<?php thm_bloginfo('name', TRUE) ?>
</span>
</div>
<?php }
add_action('thematic_header','tip_child_blogtitle',3);
In your child theme's style.css put:
#blog-title span {
position:relative;
}
#blog-title span a {
background: ; /* enter the path to your image */
width: ; /* enter the width of your image */
height: ; /* enter the approximate height of your image in ems */
min-height: ; /* enter the min-height of your image in pixels */
z-index:1;
position:absolute;
top:0;
left:0;
}
Good luck -Gene