Issues with CSS sliding doors

Hi guys I am a newbie learning css and I am right now learning the css sliding doors technique and I have come across some problem . In the CSS sliding doors article Douglas bowman changes the padding of the list element on the left with 9px and then decreases the anchor-left padding to 6px from 15 px and then makes a comment

What I can't understand is when you add a left-padding to the list element how can the inner edges of the visible doorways butt up against each other? I am not getting that point. If somebody can help me with this I will be very glad.

#header li {
    float:left;
    background:url("right.gif")
      no-repeat right top;
    margin:0;
    padding:0 0 0 9px;
    }
  #header a {
    display:block;
    background:url("left.gif")
      no-repeat left top;
    padding:5px 15px 4px 6px;
    }

HTML:

below I will give the full code he has used

 <div id="header">
    <ul>
      <li><a href="#">Home</a></li>
      <li id="current"><a href="#">News</a></li>
      <li><a href="#">Products</a></li>
      <li><a href="#">About</a></li>
      <li><a href="#">Contact</a></li>
    </ul>
  </div>

Code (markup):

 #header {
    float:left;
    width:100%;
    background:#DAE0D2 url("bg.gif")
      repeat-x bottom;
    font-size:93%;
    line-height:normal;
    }
  #header ul {
    margin:0;
    padding:10px 10px 0;
    list-style:none;
    }

#header li {
    float:left;
    background:url("left.gif")
      no-repeat left top;
    margin:0;
    padding:0 0 0 9px;
    }
  #header a, #header strong, #header span {
    display:block;
    background:url("right.gif")
      no-repeat right top;
    padding:5px 15px 4px 6px;
    }
  #header #current {
    background-image:url("left_on.gif");
    }
  #header #current a {
    background-image:url("right_on.gif");
    padding-bottom:5px;
    }

Code (markup):