Tough Time Centering Logo on Iconic One Theme

Hi,
I’m not able to center a logo at the top of the Iconic One theme. I added the necessary css on the custom.css file,

.thematic-logo {
display: block;
margin-right: auto;
margin-left: auto;
}

but the logo won’t center. It stays aligned left. I’m not sure what else I can do to center it. Any suggestions?

Tina