#sidebar{
  width:inherit;
  position: fixed;
  display: block;
}
#user_avatar{
  margin:0 auto;
  width:120px;
  height: 120px;
  border:4px solid white;
  background-color: #555;
  display: block;
  margin-top:-100px;
  position: relative;
  z-index:501;
}

#sidebar{
    width:inherit;
    position: fixed;
    display: block;
    z-index: 501;
}