nav      { flex: none; background-color: rgba(179, 199, 230, 0.6); } /* light blue, 60% opaque */
main     { flex: 6; min-width: 20em; background-color: rgba(255, 255, 255, 0.6); } /* white, 60% opaque */
aside    { flex: 4; background-color: rgba(234, 234, 234, 0.6); } /* gray, 60% opaque */

header { 
  background-color: rgba(134, 157, 199, 0.6); 
  color: #00005D; 
  padding: 2em 0 2em 10em;
  font-size: 150%;
}

footer { 
  background-color: rgba(134, 157, 199, 0.6);
  font-size: 70%;
  text-align: center;
  padding: 2em;
  clear: both;
}