<!--
So we will have an animated background with 5 clouds moving across the screen.
Steps: 
1. create the clouds
2. Animate them to move across the screen
3. Stylize the clouds(can be done as step #2 also)
-->
<div id="clouds">
  <div class="cloud x1"></div>
  <!-- Time for multiple clouds to dance around -->
  <div class="cloud x2"></div>
  <div class="cloud x3"></div>
  <div class="cloud x4"></div>
  <div class="cloud x5"></div>
</div>
<!-- Thats the markup! -->
<!-- That looks cool. We are done!! -->

/*Lets start with the cloud formation rather*/

/*The container will also serve as the SKY*/

*{ margin: 0; padding: 0;}

body {
  /*To hide the horizontal scroller appearing during the animation*/
  overflow: hidden;
}

#clouds{
  padding: 100px 0;
  background: #c9dbe9;
  background: -webkit-linear-gradient(top, #c9dbe9 0%, #fff 100%);
  background: -linear-gradient(top, #c9dbe9 0%, #fff 100%);
  background: -moz-linear-gradient(top, #c9dbe9 0%, #fff 100%);
}

/*Time to finalise the cloud shape*/
.cloud {
  width: 200px; height: 60px;
  background: #fff;
  
  border-radius: 200px;
  -moz-border-radius: 200px;
  -webkit-border-radius: 200px;
  
  position: relative; 
}

.cloud:before, .cloud:after {
  content: '';
  position: absolute; 
  background: #fff;
  width: 100px; height: 80px;
  position: absolute; top: -15px; left: 10px;
  
  border-radius: 100px;
  -moz-border-radius: 100px;
  -webkit-border-radius: 100px;
  
  -webkit-transform: rotate(30deg);
  transform: rotate(30deg);
  -moz-transform: rotate(30deg);
}

.cloud:after {
  width: 120px; height: 120px;
  top: -55px; left: auto; right: 15px;
}

/*Time to animate*/
.x1 {
  -webkit-animation: moveclouds 15s linear infinite;
  -moz-animation: moveclouds 15s linear infinite;
  -o-animation: moveclouds 15s linear infinite;
}

/*variable speed, opacity, and position of clouds for realistic effect*/
.x2 {
  left: 200px;
  
  -webkit-transform: scale(0.6);
  -moz-transform: scale(0.6);
  transform: scale(0.6);
  opacity: 0.6; /*opacity proportional to the size*/
  
  /*Speed will also be proportional to the size and opacity*/
  /*More the speed. Less the time in 's' = seconds*/
  -webkit-animation: moveclouds 25s linear infinite;
  -moz-animation: moveclouds 25s linear infinite;
  -o-animation: moveclouds 25s linear infinite;
}

.x3 {
  left: -250px; top: -200px;
  
  -webkit-transform: scale(0.8);
  -moz-transform: scale(0.8);
  transform: scale(0.8);
  opacity: 0.8; /*opacity proportional to the size*/
  
  -webkit-animation: moveclouds 20s linear infinite;
  -moz-animation: moveclouds 20s linear infinite;
  -o-animation: moveclouds 20s linear infinite;
}

.x4 {
  left: 470px; top: -250px;
  
  -webkit-transform: scale(0.75);
  -moz-transform: scale(0.75);
  transform: scale(0.75);
  opacity: 0.75; /*opacity proportional to the size*/
  
  -webkit-animation: moveclouds 18s linear infinite;
  -moz-animation: moveclouds 18s linear infinite;
  -o-animation: moveclouds 18s linear infinite;
}

.x5 {
  left: -150px; top: -150px;
  
  -webkit-transform: scale(0.8);
  -moz-transform: scale(0.8);
  transform: scale(0.8);
  opacity: 0.8; /*opacity proportional to the size*/
  
  -webkit-animation: moveclouds 20s linear infinite;
  -moz-animation: moveclouds 20s linear infinite;
  -o-animation: moveclouds 20s linear infinite;
}

@-webkit-keyframes moveclouds {
  0% {margin-left: 1000px;}
  100% {margin-left: -1000px;}
}
@-moz-keyframes moveclouds {
  0% {margin-left: 1000px;}
  100% {margin-left: -1000px;}
}
@-o-keyframes moveclouds {
  0% {margin-left: 1000px;}
  100% {margin-left: -1000px;}
}