since you wrapped the image in a link, the image is at the center of the link, instead of the page. You could wrap the whole thing in a <centre> (or a <div> with the id #menuimg) instead.
Then there must be an interference from a parent element (either .passage or #passages or #story), probably some margin/padding.
You can use the Inspect Tool (click left, bottom of the menu) of your browser to see what is affecting your image not being placed in the center.
(you can remove the doubles in css rules. whatever is set in #body for the font will be attached to any child (anything inside body))
Annnd we have it: padding: .3em .55em .25em .35em;
padding is set top → right → bottom → left. Here they are different values. So nothing will be fully centered…