@trendoman, I think that has to do with how the 'main.html' snippet calls <cms:render 'sidebar' /> - if you take a look at it you'll see that <cms:admin_css /> has already executed way before the sidebar is rendered in the body. The way things stand, It appears only the snippets contributing to the 'k_main_content' (the central part) will be able to use <cms:admin_add_css> etc.