1) animate the clouds (#clouds):
@-webkit-keyframes animClouds{
0% {background-position: 0px 102px; }
100% {background-position: -1068px 102px; }
}
#clouds {
-webkit-animation-name: animClouds;
-webkit-animation-duration: 70s;
-webkit-animation-timing-function: linear;
-webkit-animation-iteration-count: infinite;
/* is the same as */
-webkit-animation:animClouds 70s linear 0s infinite;
}
2) animate the hills (#hill2 & #hill1):
@-webkit-keyframes animHill2{
from {background-position: 0px 258px; }
to {background-position: -1110px 258px; }
}
@-webkit-keyframes animHill1{
0% {background-position: 0px 104px; }
100% {background-position: -2220px 104px; }
}
#hill2{
-webkit-animation: animHill2 25s linear 0s infinite;
}
#hill1 {
-webkit-animation: animHill1 25s linear 0s infinite;
}