<style>
#header{
    background-image: url('/montada/images/snow/s1.png'), url('/montada/images/snow/s2.png'), url('/montada/images/snow/s3.png');

    width: 100%;

    z-index:1;

    -webkit-animation: snow 10s linear infinite;

    -moz-animation: snow 10s linear infinite;

    -ms-animation: snow 10s linear infinite;

    animation: snow 10s linear infinite;
}
@keyframes snow {

  0% {background-position: 0px 0px, 0px 0px, 0px 0px;}

  50% {background-position: 500px 500px, 100px 200px, -100px 150px;}

  100% {background-position: 500px 1000px, 200px 400px, -100px 300px;}
}
@-moz-keyframes snow {

  0% {background-position: 0px 0px, 0px 0px, 0px 0px;}

  50% {background-position: 500px 500px, 100px 200px, -100px 150px;}

  100% {background-position: 400px 1000px, 200px 400px, 100px 300px;}
}
@-webkit-keyframes snow {

  0% {background-position: 0px 0px, 0px 0px, 0px 0px;}

  50% {background-position: 500px 500px, 100px 200px, -100px 150px;}

  100% {background-position: 500px 1000px, 200px 400px, -100px 300px;}
}
@-ms-keyframes snow {

  0% {background-position: 0px 0px, 0px 0px, 0px 0px;}

  50% {background-position: 500px 500px, 100px 200px, -100px 150px;}

  100% {background-position: 500px 1000px, 200px 400px, -100px 300px;}
}
</style>