How to center a vertical dropdown menu - css

Question

I am working on a new wordpress site website and running into a CSS problem with the dropdown menus. Currently they are left-aligned to the main menu or parent menu item. My preference is for them to be centered on the main menu or parent menu item.
Here is a link to the site in development: http://centraltexasdistrict.com/welcome/
Here is a link to an image, which gives an idea of what I'm looking for or trying to achieve: http://centraltexasdistrict.com/wp-content/uploads/CTD-menu.jpg
Here is the current css I'm working with:
.menu-main-container {
margin-left: auto;
margin-right: auto;
width: 690px;
padding: 0 0 0 20px;
height: 35px;
z-index: 10;
line-height: 35px;
}
.menu-main-menu-container ul li ul{ text-align:center; }
.main-navigation {
clear: both;
margin: 0 auto;
max-width: 1080px;
min-height: 36px;
position: relative;
}
#navbar {
display: block;
height: 36px;
width: 100%;
margin-top: -27px;
z-index: 10;
position: absolute;
}
#site-navigation {
padding: 0px;
height: 30px;
z-index: 10;
line-height: 30px;
float: left;
}
ul.nav-menu,
div.nav-menu > ul {
margin: 0;
padding: 0px;
}
.nav-menu li {
display: inline-block;
position: relative;
}
.nav-menu li a {
display: block;
font-family: 'Lato', sans-serif;
line-height: 30px;
color: #aaaaaa;
font-weight: 400;
text-align: center;
text-transform:uppercase;
text-decoration: none;
letter-spacing: 1px;
float: left;
font-size: 12px;
padding: 30px 7px 0px 7px;
margin-bottom: 5px;
}
.nav-menu li:hover > a,
.nav-menu li a:hover,
.nav-menu li:focus > a,
.nav-menu li a:focus {
color: #ffffff;
background-color: #353535;
}
.nav-menu .sub-menu,
.nav-menu .children {
background-color: #e07726;
padding: 0px;
position: absolute;
z-index: 99999;
overflow: hidden;
clip: rect(1px, 1px, 1px, 1px);
margin-top: 65px;
}
.nav-menu .sub-menu ul,
.nav-menu .children ul {
border-left: 0;
left: 100%;
top: 0;
}
.sub-menu {
text-align: center;
width: 100%;
left: auto;
}
.sub-menu li {
display: inline-block;
width: auto;
padding: 0px;
}
.sub-menu li a {
display: block;
height: 24px;
font-family: 'Lato', sans-serif;
line-height: 24px;
font-weight: 400;
text-align: left;
text-decoration: none;
text-transform: none;
letter-spacing: 1px;
float: left;
font-size: 11px;
padding: 2px 10px 2px 10px;
color: #ffffff;
white-space: nowrap;
}
.sub-menu li:hover > a,
.sub-menu li a:hover,
.sub-menu li:focus > a,
.sub-menu li a:focus {
background-image: none;
color: #ac5411;
background-color: transparent;
}
ul.nav-menu ul a,
.nav-menu ul ul a {
color: #fff;
margin: 0;
}
ul.nav-menu li:hover > ul,
.nav-menu ul li:hover > ul,
ul.nav-menu .focus > ul,
.nav-menu .focus > ul {
clip: inherit;
overflow: inherit;
height: inherit;
width: inherit;
}
.nav-menu .current_page_item > a,
.nav-menu .current_page_ancestor > a,
.nav-menu .current-menu-item > a,
.nav-menu .current-menu-ancestor > a {
color: /* #333333 */;
}

Answer 1

A quick solution could be to give the submenu a specified width:
ul.nav-menu li:hover > ul, .nav-menu ul li:hover > ul, ul.nav-menu .focus > ul, .nav-menu .focus > ul {
clip: inherit;
overflow: inherit;
height: inherit;
width: 200px; /* width for the submenu */
left: 50%; /* position it 50% to the left */
margin-left: -100px; /* negative margin half of with to center it */
}
Or use translate if you dont want to have a specified width (not for all old browsers and you may need some prefixes):
ul.nav-menu li:hover > ul, .nav-menu ul li:hover > ul, ul.nav-menu .focus > ul, .nav-menu .focus > ul {
clip: inherit;
overflow: inherit;
height: inherit;
transform: translate(-50%, 0);
left: 50%;
}

Answer 2

.menu-main-menu-container ul li ul{
text-align:center;
}
Add the above code in your stylesheet to center drop down list of menu bar