20px große Lücke zwischen Header und Navigation

body
{
background: url(grafiken/background.png);
font-family: sans-serif;
}
p
{
font-size: 0.8em;
text-align: justify;
}
h1
{
font-size: 1.6em;
text-align: center;
color: #03c1ff;
}
#container
{
width: 900px;
margin-left: 10%;
margin-top: 0%;
}

/* Header */

#header_container
{
background: url(grafiken/header.png);
height: 125px; width: 900px;
}


/*unebnutzte Bereiche */

#counter, #sidebar_container, #nav_heading, #nav li.subpage, #post_header, #pre_content , #title, #header, #pre_header, div.header
{visibility: hidden; width: 0px; height: 0px;}

/* Navigation */
#nav_container
{
background: url(grafiken/navoben.png);
height: 26px;
}
#nav a {text-decoration: none; color: #ffffff;}

#nav li
{
liste-style-type: none;
height: 20px;
width: 150px;
color: #ffffff;
display: block;
float: left;
text-align: center;
padding-top: 6px;
font-size: 0.9em;
text-decoration: none;
font-weight: bold;
}
#nav a:hover
{
color: #000000;
}
#nav li.checked_menu
{
background: url(grafiken/navactive.png);
}

/*Content*/

#content
{
background: #ffffff;
padding: 10px;
height: 350px;
overflow: auto;
}

#below_content
{
background: url(grafiken/footer.png);
padding-top: 15px;
padding-left: 40px;
font-size: 0.8em;
height: 25px;
}