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CSS

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CSS Base

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                .universe
  - (1..250).each do
    %div{:class => "ball"}
!

CSS 

              
                $balls: 250 ///////////////////// number of balls (default: 250)
$size: 3 //////////////////////// scale of max-size (default: 3)
$color: random /////////// CSS color of a ball (default: random)
$bg: #0F0000 /////////////// page background (default:  #0F0000)
$time: 3 ////////// velocity of movement in seconds (default: 3)
$rotateAll: false // boolean. rotate all system (default: false)

.ball
  border-top: 2px solid rgba(255,255,255,0.2)
  display: inline-block
  border-radius: 50%
  &:hover
    // do nothing
  
// balls + movement
@for $i from 1 through $balls
  @keyframes float-#{$i}
    from
      transform: translate(random(10) + em, random(5) + em)
    to
      transform: translate(random(5) + em, random(25) + em) rotate(360deg)
  .ball:nth-child(#{$i}) //
    $ballsize: $size/random(4) + em
    $transitionTime: $time * random(3)
    @if $color == random
      background: hsla(random(360), 100%, 30%,  0.6)
    @else
      background: $color
    width: $ballsize
    height: $ballsize
    @if $i < 10
      margin: 0 random(3) * $i + px
    @else
      margin: 0 $i/5 + px
    @if $transitionTime > 1
      animation: float-#{$i} ($transitionTime + s) ease-in-out infinite alternate
    @else
      animation: float-#{$i} 3s ease-in-out infinite alternate

// page decoration + rotateAll effect
@keyframes rotateAll
  to
    transform: rotate(360deg)
body
  cursor: pointer
  overflow: hidden
  background: $bg -webkit-radial-gradient(50% 40%,ellipse cover, lighten($bg, 10%), $bg 40%) no-repeat
  background: $bg -moz-radial-gradient(50% 40%,ellipse cover, lighten($bg, 10%), $bg 40%) no-repeat
.universe
  border-radius: 50%
  background: transparent
  @if $rotateAll
    animation: rotateAll 20s ease-in-out infinite
!

JS
!
999px

Console