Unable to center menu and header image twenty twelve

I have a really simple site at cyriljoyce.com on the 2012 theme

I created a child theme to center the header and menu bar but just cannot seem to make it work. The child theme text is below

The line at the bottom used to center the header image but when I changed the menu on the site it stopped working.

/*
Theme Name:     Twenty Twelve Child
Theme URI:      http://cyriljoyce.com/
Description:    Child theme for the Twenty Twelve theme
Author:         Cyril Joyce
Author URI:     http://cyriljoyce.com/about/
Template:       twentytwelve
Version:        0.1.0
*/
@import url("../twentytwelve/style.css");

.header-image { margin-left: auto; margin-right: auto; display:block; }