body {
  background-color: white;
}
 .header {
   border: 5px solid blue;
   background-color: lightblue;
   margin: auto;
   margin-top: 30px;
   width: 600px;
   height: 100px;
}
 nav{
  background-color: yellow;
  margin: auto;
  width: 600px;
  height: 60px;
}
 .main {
   border: 5px solid orange;
   background-color: grey;
   margin: auto;
   margin-top: 30px;
   margin-bottom: 30px;
   width: 600px;
   height: 750px;
}