This might come close to what you want.
Add the below code inside your theme functions.php. Then create a new css file, the filename is base on your user "login" name (i.e, login-name.css, jake.css, admin.css) then upload it within your template root directory (same location with the functions.php).
/**
* Auto include author stylesheet on WP single and custom page view.
* @author Avice D (ChaosKaizer)
* @see WP_Styles
*/
function wp_auto_include_author_css()
{ global $wp_query;
$css_path = TEMPLATEPATH.DIRECTORY_SEPARATOR;
$css_url = get_bloginfo('template_url').'/';
if ($wp_query->is_single || $wp_qeury->is_page){
$po = $wp_query->get_queried_object();
$author_name = sanitize_title_with_dashes(strtolower(get_author_name($po->post_author)));
unset($po);
$filename = $author_name.'.css';
$handle = $author_name.'-stylesheet';
if (file_exists($css_path.$filename)){
wp_register_style($handle, $css_url.$filename);
wp_enqueue_style($handle);
wp_print_styles();
}
}
}
add_action('wp_head','wp_auto_include_author_css');
If your log-in name is "John Doe" it will look for john-doe.css. Space is replace with dash and all characters is in lowercase.