Hello,
It should be auto centered in your response css file with the below CSS. But if you did change the screen width in Vertex under responsive nav to a higher number then you would also need to change it here in the s5 responsive. css file. Thats the only thing I can think of that would cause it to not show centered anymore.
.iacf_big_title {
background: rgba(0, 0, 0, 0) url("../images/iacf_line.png") no-repeat scroll center bottom;
font-size: 2.4em;
line-height: 40px;
text-align: center;
}
s5_responsive.css line 277