Apply "current_page_item" to all sections

[nfunwigabga]

Hi,
Great theme...really awesome for what I am doing. I'd like to have all the sidebar parent items open by default, but I am not having any luck with it. I have tried to do

   $output .= '<li class="' . implode( ' ', $classes ) . ' current_page_parent"><a href="' . get_permalink( self::$parent_item ) . '">' . __( 'Introduction', 'wedocs' ) . '</a></li>';
...

but it did not work. Any idea?