Circulos concentricos

HTML

<div id="outer-circle">
  <div id="inner-circle">

  </div>
</div>

CSS

#float-circle {
  
}
#outer-circle {
   border: 80px solid #a9aaab ;
   border-radius: 50%;
   height: 500px;
   width: 500px;
   position: relative;
   //opacity:0.2;
 }
 #inner-circle {
   position: absolute;
   background: #385a94;
   border-radius: 50%;
   height: 300px;
   width: 300px;
   top: 50%;
   left: 50%;
   margin: -150px 0px 0px -150px;
   //opacity:0.5;
 }