A CodePen by Tim Pietrusky. Cosmic Buttons - Inspired from "Download Button" by Cosmin Negoita http://dribbble.com/shots/641769-Download-Button

index.html

<!--
  Cosmic Buttons

  Inspired from "Download Button" by Cosmin Negoita
  http://dribbble.com/shots/641769-Download-Button
  

  2012 by Tim Pietrusky
  timpietrusky.com
-->

<section>
    <button>Cosmic</button>
    <button>Buttons</button>
</section>

style.css

* {
  -webkit-font-smoothing: antialiased;
  font-smoothing:antialiased;
}

body {
  background:#000;
}

section {
  height: 200px;
  margin: 40px auto;
  padding: 20px 0;
  width: 600px;
  text-align:center;
}

button {
  position:relative;
  border:2px solid #C54DDD;
  font:bold 20px/25px "HelveticaNeue-CondensedBold", "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", sans-serif;
  letter-spacing:-2px;
  color:#D1B7DB;
  text-shadow: 0 0 1px rgba(0, 0, 0, .5), 0 1px 1px #531F7B;
  text-transform: uppercase;
  cursor:pointer;
  
  padding:13px 35px 10px 35px;
  margin:0px 60px;
  border-radius:100px;
  
  box-shadow: 
    inset 0 -2px 6px 3px #B348CC,
    0 -1px 1px rgba(158, 100, 166, .5),
    0 2px 3px rgba(0, 0, 0, .5),
    0 0 0 10px rgba(60, 60, 60, .2)
  ;
  
  background-color:rgb(67, 26, 76, .5);

  background: linear-gradient(left,  rgba(167,64,180,.3) 0%, rgba(124,48,161,.3) 85%, rgba(165,64,183,.3) 99%),
      linear-gradient(left, rgba(167,64,180,0) 0%, rgba(240,240,240,0) 92%, rgba(240,240,240,.1) 99%),
      linear-gradient(right, rgba(167,64,180,.3) 0%, rgba(124,48,161,.3) 85%, rgba(165,64,183,.3) 99%),
      linear-gradient(right, rgba(167,64,180,0) 0%, rgba(240,240,240,0) 96%, rgba(240,240,240,.1) 99%),
      linear-gradient(top,   rgba(167,64,180,0) 0%,rgba(124,48,161,1) 75%, rgba(197, 77, 221, .7) 95%);
  
  transition: all .337s ease-in-out;
}

button:before {
  position:absolute;
  bottom:-12px;
  left:15%;
  z-index:-1;
  content:'';
  height:50%;
  width:70%;
  
  background: linear-gradient(left, rgba(44,11,64,0) 0%, rgba(44,11,64,.7) 20%, rgba(83,20,122,.8) 50%, rgba(44,11,64,.7) 80%, rgba(44,11,64,0) 100%);

}

button:after {
  position:absolute;
  top:-62.5%;
  left:-37.5%;
  z-index:-1;
  content:' ';
  height:225%;
  width:175%;

  background: radial-gradient(center, ellipse cover,  rgba(83,20,121,.2) 0%,rgba(0,0,0,1) 75%);
}

button:hover {
  color:#fff;
  
  box-shadow: 
    inset 0 -2px 6px 3px #B348CC,
    0 -1px 1px rgba(158, 100, 166, .5),
    0 2px 3px rgba(0, 0, 0, .5),
    0 2px 3px rgba(67, 26, 76, .7),
    0 0 0 14px rgba(67, 26, 76, .3),
    0 0 0 8px rgba(67, 26, 76, .2)
  ;
  
  background-color:rgba(255, 255, 255, .25);
}