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@import "compass";
/* Variables */
$green: #33B679;

@-webkit-keyframes fill {
  to { width: 100%; }
}
@-moz-keyframes fill {
  to { width: 100%; }
}
@-o-keyframes fill {
  to { width: 100%; }
}
@keyframes fill {
  to { width: 100%; }
}

body { padding: 50px; }

/* Typography */
h1, p {
  font-family: sans-serif;
  text-align: center;
}

h1 { padding-bottom: 12px; }
p { color: #CCC; }

/* Button */
.button {
  background: $green;
  display: block;
  height: 60px;
  font-family: sans-serif;
  font-size: 20px;
  font-weight: 100;
  margin: 50px auto;
  position: relative;
  width: 185px;
  
  &:before {
    color: #FFF;
    content: attr(name);
    height: 100%;
    line-height: 3.1;
    position: absolute;
    text-align: center;
    width: 100%;
    z-index: 10;
  }
  
  &:after {
    background: rgba(0,0,0,0.15);
    content: '';
    height: 100%;
    position: absolute;
    width: 0;
  }
  
  &:hover {
    cursor: pointer;
  }
}

.button.animation {
  &:after {
    -webkit-animation: fill .5s forwards ease-out;
    -moz-animation: fill .5s forwards ease-out;
    -o-animation: fill .5s forwards ease-out;
    animation: fill .5s forwards ease-out;
    left: 0;
    top: 0;
    z-index: 5;
  }
}

$('.button').click(function() {
  $(this).toggleClass('animation');
});

<h1>Submit Animation</h1>
<p>Utilizing the power of :before and :after pseudo-elements.</p>
<span class="button" name="Submit"></span>