css drop down menu problem

hi,
I have this problem with a drop down menu code I found online. When the horizontal menu (on top of page) drops down the rest of the content that is in the same site moves down for a space equal to the height of the drop down list. Any idea how can i fix this?
the css i found is the following

[CODE]
body {
margin: 0;
padding: 0;
font: 80% verdana, arial, sans-serif;
}
dl, dt, dd, ul, li {
margin: 0;
padding: 0;
list-style-type: none;
}
#menu {
position: relative; /* Menu position that can be changed at will */
top: 0;
left: 0;
z-index:100;
width: 100%; /* precision for Opera */
}
#menu dl {
float: left;
width: 12em;
}
#menu dt {
color:#f2f2e6;
cursor: pointer;
text-align: center;
font-weight: bold;
background: #00592d;
border: 1px solid gray;
margin: 1px;
}
#menu dd {
display: none;
border: 1px solid gray;
}
#menu li {
text-align: center;
background: #fff;
position: relative;
}
#menu li a, #menu dt a {
color: #f2f2e6;
text-decoration: none;
display: block;
height: 100%;
border: 0 none;
}
#menu li a:hover, #menu li a:focus, #menu dt a:hover, #menu dt a:focus {
color:#00592d;
background: #eee;
}
#site {
position: absolute;
z-index: 1;
top : 70px;
left : 10px;
color: #000;
background-color: #ddd;
padding: 5px;
border: 1px solid gray;
}
[/CODE]

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