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HTML 

              
                <div class="block">
  <h1>OuroboroCSS</h1>

<p class="circle">
  <span class="ouro">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>

  <span class="ouro ouro2">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>

  <span class="ouro ouro3">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>
</p>

<p class="round">
  <span class="ouro">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>

  <span class="ouro ouro2">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>

  <span class="ouro ouro3">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>
</p>

<p class="double">
  <span class="ouro">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>

  <span class="ouro ouro2">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>

  <span class="ouro ouro3">
    <span class="left"><span class="anim"></span></span>
    <span class="right"><span class="anim"></span></span>
  </span>
</p>

  <p class="info"><a href="http://en.wikipedia.org/wiki/Ouroboros">Why the name OuroboroCSS?</a><br /><a href="https://twitter.com/geoffrey_crofte">by @geoffrey_crofte</a></p>
</div>
!

CSS 

              
                /* Inspirated from  http://www.alessioatzeni.com/wp-content/tutorials/html-css/CSS3-loading-animation-loop/index.html */
.ouro {
    position: relative;
    display:inline-block;
    height: 46px;
    width: 46px;
    margin: 1em;
    border-radius: 50%;  
    background: none repeat scroll 0 0 #DDDDDD;
    overflow:hidden;
    box-shadow: 0 0 10px rgba(0,0,0,.1) inset, 0 0 25px rgba(0,0,255,0.075);
}

.ouro:after {
    content: "";
    position: absolute;
    top: 9px; left: 9px;
    display: block;
    height: 28px; width: 28px;
    background: none repeat scroll 0 0 #F2F2F2;
    border-radius: 50%;
    box-shadow: 0 0 10px rgba(0,0,0,.1);
}
.ouro > span {
    position: absolute;
    height: 100%; width: 50%;
    overflow: hidden;
}
.left  { left:0   }
.right { left:50% }

.anim {
    position: absolute;
    left: 100%; top: 0;
    height: 100%; width: 100%;
    border-radius: 999px;
    background: none repeat scroll 0 0 #508EC3;
    opacity: 0.8;
    -webkit-animation: ui-spinner-rotate-left 3s infinite;
    animation: ui-spinner-rotate-left 3s infinite;
    -webkit-transform-origin: 0 50% 0;
    transform-origin: 0 50% 0;
}
.left .anim {
    border-bottom-left-radius: 0;
    border-top-left-radius: 0;
}
.right .anim {
    border-bottom-right-radius: 0;
    border-top-right-radius: 0;
    left: -100%;
    -webkit-transform-origin: 100% 50% 0;
    transform-origin: 100% 50% 0;
}

/* v2 */
.ouro2 .anim {
   -webkit-animation-delay:0;
   animation-delay:0;
}
.ouro2 .right .anim{
   -webkit-animation-delay: 1.5s;
   animation-delay: 1.5s;
}

/* v3 */
.ouro3 .anim {
   -webkit-animation-delay: 0s;
   -webkit-animation-duration:3s;
   -webkit-animation-timing-function: linear;
   animation-delay: 0s;
   animation-duration:3s;
   animation-timing-function: linear;
}
.ouro3 .right .anim{
   -webkit-animation-name: ui-spinner-rotate-right;
   -webkit-animation-delay:0;
   -webkit-animation-delay: 1.5s;
   animation-name: ui-spinner-rotate-right;
   animation-delay:0;
   animation-delay: 1.5s;
}

/* round variation */
.round .ouro:after {display:none }

/* double variation */
.double .ouro:after {
  height: 13px; width: 13px;
  left: 7px; top: 7px;
  border: 10px solid #ddd;
  background: transparent;
  box-shadow: none;
}

@keyframes ui-spinner-rotate-right{
  0%{transform:rotate(0deg)}
  25%{transform:rotate(180deg)}
  50%{transform:rotate(180deg)}
  75%{transform:rotate(360deg)}
  100%{transform:rotate(360deg)}
}
@keyframes ui-spinner-rotate-left{
  0%{transform:rotate(0deg)}
  25%{transform:rotate(0deg)}
  50%{transform:rotate(180deg)}
  75%{transform:rotate(180deg)}
  100%{transform:rotate(360deg)}
}

@-webkit-keyframes ui-spinner-rotate-right{
  0%{-webkit-transform:rotate(0deg)}
  25%{-webkit-transform:rotate(180deg)}
  50%{-webkit-transform:rotate(180deg)}
  75%{-webkit-transform:rotate(360deg)}
  100%{-webkit-transform:rotate(360deg)}
}
@-webkit-keyframes ui-spinner-rotate-left{
  0%{-webkit-transform:rotate(0deg)}
  25%{-webkit-transform:rotate(0deg)}
  50%{-webkit-transform:rotate(180deg)}
  75%{-webkit-transform:rotate(180deg)}
  100%{-webkit-transform:rotate(360deg)}
}

/*
 * Some bugs with Chrome (Android), Safari and Opera, I'll try to see how http://atomeye.com/projects/sass-css-spinner.html made his code.
 */

/* presentation styles */
html {height: 100%}
body { text-align:center; background: radial-gradient(circle, #fff 0%, #bbb 85%) no-repeat; background: -webkit-radial-gradient(circle, #fff 0%, #bbb 85%) no-repeat; height: 100%; display:table; width:100%}
.block {display: table-cell; vertical-align:middle}
h1, a { margin-top: 1em; font-family: "Open Sans Light", "Open Sans", "Segoe UI", Helvetica, Arial; color: #888; font-weight: lighter;}
.info {margin-top: 25px}
.info a {font-size: 12px; color: #999}
.info br + a {text-decoration:none}
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JS
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999px

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