#content { display: flex; }
nav      { flex: none; }
main     { flex: 6; min-width: 20em; }
aside    { flex: 4; } 

nav   { order: 1; }
main  { order: 2; }
aside { order: 3; } 
		
* { box-sizing: border-box; margin: 0; }
body {
  margin: 0;
  padding: 0;
  font-family: Verdana, Arial, sans-serif;
   background-size: cover; 
  color: #00005D;
}
nav ul {
  list-style: none;  
  margin: 0;
  padding: 0;
}

nav li {
  display: inline-block;   
  margin-right: 1em;       
}