main.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;
  padding-left: 160px;
}

nav {
  position: fixed;
  top: 0;
  left: 0;
  width: 146px;
  height: 100%;
  background-color: #CCCCCC;
  border-right: 2px solid #888;
}

nav ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

nav ul li {
  padding: 10px 10px 10px 15px;
  border-bottom: 1px solid gray;
}

nav ul li a {
  color: #444;
  text-decoration: none;
}

nav ul li a:hover {
  color: gray;
}