Try to use srcset but no luck

[Allmedialab]

Hi, Try to use srcset, but unfortunately I don't get it to work! <div class="hero unit"> <div class="unit__inner" data-parallax data-parallax-bottom data-parallax-factor="3"> <h1 class="text-center">Hong Kong</h1> <p class="text-center">Pictures by <a href="http://cfremdt.de/">Christoph Fremdt</a></p> </div> <div class="background" data-parallax data-parallax-top> <img src="img/hongkong-1.jpg" srcset=" /img/hongkong-resp/hongkong-1_uclu5m_c_scale%2Cw_400.jpg 400w, /img/hongkong-resp/hongkong-1_uclu5m_c_scale%2Cw_948.jpg 948w, /img/hongkong-resp/hongkong-1_uclu5m_c_scale%2Cw_1343.jpg 1343w, /img/hongkong-resp/hongkong-1_uclu5m_c_scale%2Cw_1920.jpg 1920w"> </div> </div> All suggestions to accomplish this are more then welcome! Regards & Thanks, David