Images are, by default, centered in their container and fill the max dimension, so something in your custom css is causing the image to not be centered. I tried removing all the custom css and get
For the image, it looks like your custom rule is not specific enough to overcome the rule in the xmatter, so you can do .A6Portrait.outsideFrontCover .marginBox img { max-width: unset; }
or .A6Portrait .marginBox img { max-width: unset !important; }