Gallery's images are shifted to the right

Hello everybody.
I’m using Minimatica, and all the pictures I post are shifted to the right.
how can I fix that?
here the website :
http://mesiah.fr/conceptart/

When I post I put the picture in “featured image” and then I select the “thumbnail” option then I click on insert into post.
The image is showed but shifted.

thanks a lot for this theme.