Concentric traingles
HTML
<div class="outer circle border_color">
<div class="inner circle border_color">
</div>
</div>
CSS
.border_color{
border-radius : 50%;
}
.circle {
border: 1px solid red;
}
.outer{
background-color:blue;
width:400px;
height:400px;
position:relative;
}
.inner{
width:94%;
position:relative;
height:94%;
top:3%;
left:3%;
background-color:green;
}