Background-image size fixed cover which doesn't work properly on iOS, since it uses the height of the document and not the viewport.

    body {
      /* cover sized and fixed backgrounds are handled wrongly in iOS */
      background: url(https://newevolutiondesigns.com/images/freebies/nature-hd-background-9.jpg) no-repeat center center fixed;
      -webkit-background-size: cover;
      -moz-background-size: cover;
      -o-background-size: cover;
      background-size: cover;
    }
  

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See Github repo

More info at stackoverflow.com

Live demo at Doklist.com, Doklist.com.br

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