All your css stylefiles must be loaded over ssl. Just look on your console or sourcecode and make sure all files are loaded over https
Example:
http://pilotlounge.vairleasing.net/lib/css/phpvms.css http://pilotlounge.vairleasing.net/lib/skins/elmer/vendors/bower_components/datatables/media/css/jquery.dataTables.min.css http://pilotlounge.vairleasing.net/lib/skins/elmer/vendors/bower_components/jquery-toast-plugin/dist/jquery.toast.min.css