MediaWiki:Common.css

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/* CSS placed here will be applied to all skins */
#ca-watch { display: none !important; }
#ca-talk { display: none !important; }
<?php global $wgUser; if( $wgUser->isAnon() ) { ?>
      <style type="text/css">
        #ca-viewsource { display: none !important; }
      </style> 
    <?php } ?>