You've tried everything but not position: absolute;
which is an appropriate way to go for.. In the snippet below, I used left: 50%;
to first position the logo in the center but still it isn't centered, so I negated 1/2 the size of the image which is 75px
in width
so I used -38px
img#logo-nav {
max-width: 75px;
position: absolute;
left: 50%;
margin-left: -38px;
}