Why is my ul misbehaving?

You can see my problem highlighted in green at my URL http://www.fosterdesignomaha.com. For some reason there’s an odd indentation to the left of my ul. Below is my style sheet. This is a theme I’m building from scratch.

.mainContainer {
width: 960px;
margin-left: auto;
margin-right: auto;
background-color: pink;
}

.customIndex {
width: 720px;
background-color: yellow;
float: right;
}

.customSidebar {
width: 240px;
background-color: green;
float: left;
left: 0%;
}

.customSidebar ul {
text-align: center;
list-style-type: none !important;
}

.customSidebar ul li {
border: 1px solid #000;
}

.customFooter {
background-color: blue;
clear: left;
padding: 10px;
}