Two columns gallery doesn't match with other elements width

[Axinet]

In editor 2 columns gallery has the exact same width as image inserted alone:

On frontend page view there is a visible width difference on the right side (marked with the red box):

[karmatosed]

Do you get the same issue with just the twenty seventeen or any default theme? I'm thinking this isn't the theme.

[Axinet]

Yes, twenty seventeen has the exact same issue on frontend view. You are right - it is related to css selector .wp-block-gallery .blocks-gallery-image from /wp-content/plugins/gutenberg/blocks/build/style.css