Not sure why the opening menu works in Firefox but fails in Internet Explorer.

In IE it is not centered, even though I'm using margin-left, margin-right: auto

develop.pariscut.com

.menu-vertical {
font-size: 1.5em;
font-weight: bold;
margin-left: auto;
margin-right: auto;
opacity: 0.8;
position: relative;
top: -450px;
width: 28% !important;
z-index: 99;
}