var ns4 = (document.layers) ? true : false;

  var agt = navigator.userAgent.toLowerCase();

  var is_sun = (agt.indexOf("sunos")!=-1);



  var url_root = 'http://www.rssd.esa.int/';
  var hsc_root = 'SA-general/Projects/Herschel.rob/';
  var css_root = 'Tpl/Assets/Style/';

  var url_complete = '<link rel="stylesheet" href="'+ url_root + hsc_root + css_root +'ns4_sun.css">'

  if (ns4 && is_sun) {

    document.write(url_complete);

  }