Header image keeps center as page shrinks, but logo does not

I have set my header image to align top center, so if I resize the page to be smaller (in my browser), the image shifts with the page so I always see the center-most section. However, the logo being displayed above it does not behave this way. It seems to be tied to the upper left, so as the window shrinks, we see less and less of the right-hand part of the logo.

Any way to make the logo also hang in the center?