ex1.css

.container {
  /*
    If you have a block-level element of a certain width, margin: 0 auto;
    will how you center it inside its parent container.

    See: http://bluerobot.com/web/css/center1.html
    
    Don't change the container width.
  */
  margin: 0 auto;  
  width: 720px;
}

nav { 
}
ul {
  list-style: none;
  width: 100%;
  padding-left: 0;
  border-radius: 5px;
  border: 1px solid gray;
  background: linear-gradient(silver, gray);
}

ul a { 
  text-decoration: none;
  color: #444666;
}

li { 
  display:inline-block;
  width: 19.7%;
  
  border-right: 1px solid white;
  padding-top: 10px;
  padding-bottom: 10px;
  text-align: center;
  margin-right: -3px;
}

li:last-child { 
  border-right: 0;
}