Hello Jeff,
Thanks for take your time provide this screenshot.
I have consult with our designer, it seems like that parent class already do the float: left, so that you have apply this following css block code and see how it goes?
.theme-nav .navbar-main > ul {
float: none !important;
display: inline-block;
}
.theme-nav .navbar-main {
text-align: center;
}
.theme-nav .navbar-main > ul > li {
margin: 0 15px !important;
}