Add this to your css
.site-header .site-title a{
background-position: center !important;
}
That should do it.
Also, if you want to add more height to your logo (since it appears to be cutoff), then you can look at line 2057 and adjust the min-height
from 164px to around 240px –
.header-image .site-title a {
float: none;
min-height: 240px;
width: 100%;
}