SOURCE

<div class="content">
  <div class="box"></div>
</div>

.content { 
	width: 100px; 
   	height: 100px; 
    box-sizing: border-box; 
    padding: 5px; 
    border-radius: 50%; 
    background-image: -webkit-linear-gradient(top, red 0%, blue 30%, yellow 60%, green 90%);  
    background-image: -moz-linear-gradient(top, red 0%, blue 30%, yellow 60%, green 90%); 
    background-image: linear-gradient(top, red 0%, blue 30%, yellow 60%, green 90%);  
}
.box { 
	width:100%; 
    height:100%; 
    border-radius:50%; 
    background:#fff; 
}