<div id="background-wrap">
    <div class="x1">
        <div class="cloud"></div>
    </div>

    <div class="x2">
        <div class="cloud"></div>
    </div>

    <div class="x3">
        <div class="cloud"></div>
    </div>

    <div class="x4">
        <div class="cloud"></div>
    </div>

    <div class="x5">
        <div class="cloud"></div>
    </div>
</div>

body {
  background: #00b4ff;
  color: #333;
  font: 100% Arial, Sans Serif;
  height: 100vh;
  margin: 0;
  padding: 0;
  overflow-x: hidden;
}

#background-wrap {
    bottom: 0;
  left: 0;
  padding-top: 50px;
  position: fixed;
  right: 0;
  top: 0;
  z-index: -1;
}

/* KEYFRAMES */

@-webkit-keyframes animateCloud {
    0% {
        margin-left: -1000px;
    }
    100% {
        margin-left: 100%;
    }
}

@-moz-keyframes animateCloud {
    0% {
        margin-left: -1000px;
    }
    100% {
        margin-left: 100%;
    }
}

@keyframes animateCloud {
    0% {
        margin-left: -1000px;
    }
    100% {
        margin-left: 100%;
    }
}

/* ANIMATIONS */

.x1 {
  -webkit-animation: animateCloud 35s linear infinite;
  -moz-animation: animateCloud 35s linear infinite;
  animation: animateCloud 35s linear infinite;
  
  -webkit-transform: scale(0.65);
  -moz-transform: scale(0.65);
  transform: scale(0.65);
}

.x2 {
  -webkit-animation: animateCloud 20s linear infinite;
  -moz-animation: animateCloud 20s linear infinite;
  animation: animateCloud 20s linear infinite;
  
  -webkit-transform: scale(0.3);
  -moz-transform: scale(0.3);
  transform: scale(0.3);
}

.x3 {
  -webkit-animation: animateCloud 30s linear infinite;
  -moz-animation: animateCloud 30s linear infinite;
  animation: animateCloud 30s linear infinite;
  
  -webkit-transform: scale(0.5);
  -moz-transform: scale(0.5);
  transform: scale(0.5);
}

.x4 {
  -webkit-animation: animateCloud 18s linear infinite;
  -moz-animation: animateCloud 18s linear infinite;
  animation: animateCloud 18s linear infinite;
  
  -webkit-transform: scale(0.4);
  -moz-transform: scale(0.4);
  transform: scale(0.4);
}

.x5 {
  -webkit-animation: animateCloud 25s linear infinite;
  -moz-animation: animateCloud 25s linear infinite;
  animation: animateCloud 25s linear infinite;
  
  -webkit-transform: scale(0.55);
  -moz-transform: scale(0.55);
  transform: scale(0.55);
}

/* OBJECTS */

.cloud {
  background: #fff;
  background: -moz-linear-gradient(top,  #fff 5%, #f1f1f1 100%);
  background: -webkit-gradient(linear, left top, left bottom, color-stop(5%,#fff), color-stop(100%,#f1f1f1));
  background: -webkit-linear-gradient(top,  #fff 5%,#f1f1f1 100%);
  background: -o-linear-gradient(top,  #fff 5%,#f1f1f1 100%);
  background: -ms-linear-gradient(top,  #fff 5%,#f1f1f1 100%);
  background: linear-gradient(top,  #fff 5%,#f1f1f1 100%);
  filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#fff', endColorstr='#f1f1f1',GradientType=0 );
  
  -webkit-border-radius: 100px;
  -moz-border-radius: 100px;
  border-radius: 100px;
  
  -webkit-box-shadow: 0 8px 5px rgba(0, 0, 0, 0.1);
  -moz-box-shadow: 0 8px 5px rgba(0, 0, 0, 0.1);
  box-shadow: 0 8px 5px rgba(0, 0, 0, 0.1);

  height: 120px;
  position: relative;
  width: 350px;
}

.cloud:after, .cloud:before {
    background: #fff;
  content: '';
  position: absolute;
  z-indeX: -1;
}

.cloud:after {
  -webkit-border-radius: 100px;
  -moz-border-radius: 100px;
  border-radius: 100px;

  height: 100px;
  left: 50px;
  top: -50px;
  width: 100px;
}

.cloud:before {
  -webkit-border-radius: 200px;
  -moz-border-radius: 200px;
  border-radius: 200px;

  width: 180px;
  height: 180px;
  right: 50px;
  top: -90px;
}