body {
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
    
    height: 932px;
    
}

.topnav {
  overflow: hidden;
  background-color: #3CB371;
  height: 50px;
    }

.topnav a {
  float: center;
  color: black;
  padding: 10px 12px;
  text-decoration: none;
  font-size: 16px;
  height: 50px;
}

.topnav a:hover {
  background-color: #90EE90;
  color: black;
  height: 50px;
}

.topnav a.active {
  background-color: #90EE90;
  color: white;
  height: 50px;
}


.mainDIV{
    position:relative;
    background:yellow;
    width:100%;
    min-width:315px;
  height: 50px;
}
.leftDIV{
    position:absolute;
    top:0px;
    left:0px;
    height:50px;
    width:100px;
    background:red;
}
.middleDIV{
    height:50px;
    width:100px;
    background:blue;
    margin:0px auto;
}
.rightDIV{
    position:absolute;
    top:0px;
    right:0px;
    height:50px;
    width:100px;
    background:green;
}