Making an unordered list stretch horizontally so as to always fill up a div

Making an unordered list stretch horizontally so as to always fill up a div

Sorry about this, I thought this issue was resolved, but then it turned
out that it wasn't.
I have an unordered list inside a div, and I want the list to always fill
up the entire div horizontally, no matter what the zoom level. How does
one go about this? Set the width of each list item individually? I tried
this, and the widths of my items do add up to 100%, yet the list still
does not fill up the div. I'm modifying a template, too, so much of the
HTML is hidden from me, but I can edit CSS all I want to. What else can I
do in terms of CSS? Padding? Something involving the calc function? I've
experimented with all of these, but somehow nothing seems to work.
Are there any other ideas as to how this can be done