/* Change WordPress dashboard CSS */
function custom_admin_styles() {
echo '<style type="text/css">#wphead{background:#069}</style>';
}
add_action('admin_head', 'custom_admin_styles');
function custom_admin_styles() {
echo '<style type="text/css">#wp-admin-bar-new-content{display:none;}</style>';
echo '<style type="text/css">#wp-admin-bar-comments{display:none;}</style>';
echo '<style type="text/css">#wp-admin-bar-wp-logo{display:none;}</style>';
echo '<style type="text/css">#screen-meta-links{display:none;}</style>';
}
You can add any changes to the css between the tags.