anchor.diff:  
   // header...
   header {
  -  background: #eee;
  +  background: $light_gray;
     padding: 1em 0;
   
     h1,
  
positive.code: 
    .current,
    a {
      border: 1px solid #ccc;
      line-height: 100%;
      margin: 0;
      padding: .5em;
  
negative.code:     margin: 6px 14px 0 0;
      height: 200px;
      width: 136px;
      outline: 1px solid $medium_gray;
  
      & a:hover {
        background: none;
  