Centering div over slider

Hello :-)

Hoping some fresh eyes will be able to help me out. I am trying to put a static title over the top of a slider, but centered both horizontally and vertically. I thought I had cracked it but realised it's not quite central vertically. Can anyone see where I am going wrong?

Live URL here.

Css is:

#portfolio-single-gallery{
	position: relative;
    top: 0;
    left: 0;
    width: 100%;}
	
.title-overlay{
    top: 50%;
	width:100%;
	text-align:center;
	z-index:99;
	position: absolute;}
	
.title-overlay h1{
	color:#fff;}
	
#portfolio-single-gallery .slider-nav{
	margin:20px 0px;
        z-index: 10;
        width: 100%;}