<div>
<input type="checkbox" name="choice1" checked />
<input type="checkbox" name="choice2" class="error" />
</div>

<!--
class "error" is used to change gray color to red
two different style, which is your favorite?
-->

div{
  margin: 0 auto;
  margin: 80px 0;
  text-align: center;  
}

input[type='checkbox'] {
  display:block;
  margin: 0 auto;
  margin-bottom: 10px;
  -webkit-appearance: button;
  border:none;
  background: url(http://www.pixelslip.be/img/check.png) no-repeat 0 0 transparent;
  background-color: #ccc;
  width: 90px;
  height: 40px;
  border-radius: 3px;
  box-shadow: inset 0 1px 4px rgba(0,0,0,.2);
  cursor: pointer;
  position: relative;
  transition: background-color 1s;
}
input[type='checkbox'].error{
   background-color: #c63d3d;
}
input[type='checkbox']:after{
  content: "";
  display: block;
  position: absolute;
  top: 0;
  left: 0;
  width: 45%;
  height: 80%;
  background-color: #fdfdfd;
  margin: 4%;
  border-radius: 3px;
  box-shadow: 0 1px 2px rgba(0,0,0,.2);
  
  background: rgb(255,255,255);
background: -moz-linear-gradient(top,  rgba(255,255,255,1) 0%, rgba(243,243,243,1) 100%);
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(255,255,255,1)), color-stop(100%,rgba(243,243,243,1)));
background: -webkit-linear-gradient(top,  rgba(255,255,255,1) 0%,rgba(243,243,243,1) 100%);
background: -o-linear-gradient(top,  rgba(255,255,255,1) 0%,rgba(243,243,243,1) 100%);
background: -ms-linear-gradient(top,  rgba(255,255,255,1) 0%,rgba(243,243,243,1) 100%);
background: linear-gradient(to bottom,  rgba(255,255,255,1) 0%,rgba(243,243,243,1) 100%);
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#ffffff', endColorstr='#f3f3f3',GradientType=0 );

 transition: .5s all;
}

input[type='checkbox']:checked{
  background-color: #79d122;
} 

input[type='checkbox']:checked:after {
  left: 45%;
}

/* webkit optimisation - just css */