This is the same with adding a banner before and after (bottom-most part) the footer area.
This is interesting.
In requires, of course, coding. To be able to add banner images below your header, check out wp_head action. Like:
<?php
add_action('wp_head', 'add_header_banner');
function add_header_banner() {
echo '<img src="#" alt=""';
}
Of course, it will be more complicated than that... if you want admin interface etc.
?>
For the content, you need to add_filter on the_content here.
To give each category a different banner, you’ll use is_category here and probably switch statements and the like.
Are you referring to fixing it to the top of your browser? Like position it fixed?
You can create your own template with a sidebar and have it done with css, js and php. Or you can install a free theme with a built-in sidebar and code from there.