can i revert to earlier stylesheet?

hello
I have been looking online and on though my site to figure out a way to fix my mistake but have not found the error. i apologize for being such an html novice!

I was trying to get rid of the pesky border in my blog. so to figure out what did what i would change something – see what it did and then change it back.
so i went to the stylesheet and changed this bit near the bottom:

‘}

.nav ul ul li {
width: 100px;
background-color: #fff;
float: left;
display: block;
position: relative;
z-index: 30;
border-bottom: 1px solid black;
}’

so that it said ‘border-bottom: 0px solid black;’ where it says ‘border-bottom: 1px solid black;’

Though this really does not seem to have anything to do with the background color, it made everything go black. so i went back and changed it back to what it had said previously and the background was still BLACK!! eek!

i have since discovered that i have somehow made it so that when my Highlight Font Color is Black – so it my background color. at the moment both are white – which makes it impossible to read the headlines but as least the body text is visible.

if you can offer any help to get it back as it was i would definitely appreciate it. i have also tried restoring an earlier version of my site through dreamhost but it still looks the same.

many thanks!