Problem with Drop Down Menu

I have a javascript drop down menu throughout my site, i have a problem with the positioning in different resolution.

<script>

function expand(s, m)
{
var browser = window.navigator.appName;
var dif = 0;
if (browser != “Microsoft Internet Explorer”) { dif = 12; }

var d = document.getElementById(m);
var td = document.getElementById(s);
var left = td.offsetLeft + 50;
var top = td.offsetTop + 108;
var width = td.offsetWidth – dif;

td.style.color = “#FFFFFF”;

d.style.top = top;
d.style.left = left;
d.style.width = width;
d.style.position = “absolute”;
d.style.visibility = “visible”;
d.style.display = “block”;
}

function collapse(s, m)
{
var d = document.getElementById(m);
var td = document.getElementById(s);

td.style.color = “black”;

d.style.position = “static”;
d.style.visibility = “hidden”;
d.style.display = “none”;
}

function collapseAll()
{
var menuDiv = document.getElementById(“menu”);
var divs = menuDiv.getElementsByTagName(“div”);
var div;

for (i = 0; i < divs.length; i++)
{
div = divs[i];
div.style.visibility = “hidden”;
div.style.display = “none”;
}
}
</script>

var left = td.offsetLeft + 50; this lines states were the drop down is positioned from the left hand side, i need this to be constant whatever resolution it is at?

Any Ideas?

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