Fixed position Dropdownbox menu

Dear all.

I have a question. I want a fixed position for this drop down box menu

Can someone help me?

#nav{
list-style:none;
text-decoration: none;
font-size: 14px;
font-family: "Trebuchet MS", Arial, Helvetica, sans-serif;
margin-bottom:10px;
/* Clear floats */
float:left;
width: 100%;
height: 30px;
margin-left: -30px;
/* Bring the nav above everything else--uncomment if needed.*/
position: relative;
z-index: 5;
}
#nav li{
float:left;
position: relative;
text-decoration: none;
}
#nav a{
display:block;
padding:5px;
color:#fff;
background:#5e5838;
width: 135px;

}
#nav a:hover{
color:#fff;
background:#322f20;
}

/*--- DROPDOWN ---*/
#nav ul{
background:#fff; /* Adding a background makes the dropdown work properly in IE7+. Make this as close to your page's background as possible (i.e. white page == white background). */
background:rgba(255,255,255,0); /* But! Let's make the background fully transparent where we can, we don't actually want to see it if we can help it... */
list-style:none;
position: absolute;
margin-left: -40px;
left:-9999px; /* Hide off-screen when not needed (this is more accessible than display:none */
}
#nav ul li{
padding-top:1px; /* Introducing a padding between the li and the a give the illusion spaced items */
float: none;
}
#nav ul a{
white-space:nowrap; /* Stop text wrapping and creating multi-line dropdown items */
}
#nav li:hover ul{ /* Display the dropdown on hover */
left:0; /* Bring back on-screen when needed */
}
#nav li:hover a{ /* These create persistent hover states, meaning the top-most link stays 'hovered' even when your cursor has moved down the list. */
background:#322f20;
text-decoration: none;
}
#nav li:hover ul a{ /* The persistent hover state does however create a global style for links even before they're hovered. Here we undo these effects. */
text-decoration:none;
}
#nav li:hover ul li a:hover{ /* Here we define the most explicit hover states--what happens when you hover each individual link. */
background:#333;
}


Regards,

William

Depending on where you want it positioned I would say a good place to start is in #nav

do



if you want it fixed, so when scrolling content the menu remains on top do