How to attach a div to the side of a div positioned via margin: auto 0;

[erikabuffalo]

I have what is a fairly common page layout where the content div is centralised on the page using \[code\]margin:auto 0\[/code\]. The width of the div itself varies depending on available page width.I want another div featuring a logo to 'stick' to the outside left hand side of this div (ie no gap or overlap between the two) at a fixed height. What CSS should I use for this?