CSS problem with the [file] shortcut

Attempting to create a front page for my archive, displaying 2 images that will link to further pages. The images are uploaded and I use this shortcode:
[file id=36 size=fullsize link_file=0]

What comes back is a shrunken version of the image, and it seems that the item-file img in the CSS is setting a height to 6em. I don't want any imposed height as I know how big my images are.

Is this a bug?

That should, of course, read [file] shortcode - apologies

The shortcodes themselves generally don't apply much or any CSS. If there's a max-width or max-height being applied, it would be something coming from your theme, and you'd change or remove it there.