Add --ignore-ssl-errors=true when running phantomjs to ignore warnings like this.
2016-10-27T14:31:37 [DEBUG] Network - SSL Error: "The issuer certificate of a locally looked up certificate could not be found"
2016-10-27T14:31:37 [DEBUG] Network - SSL Error: "The root CA certificate is not trusted for this purpose"
2016-10-27T14:31:37 [DEBUG] Network - Resource request error: QNetworkReply::NetworkError(SslHandshakeFailedError) ( "SSL handshake failed" ) URL: "https://www.example.com/styles.css"