[Theme: Arcade Basic] Change certain pages width

Hi everyone! It’s my first post, so I may not be very cleau when explaining my problem, please forgive me!

So, on my website I would like to display most of my pages as they are (with a sidebar) and 3 of them (the 3 submenus under “galleries”) without widgets and in full width (or more precisely in full width, with the same spacing they have on the left)

For now I managed to hide the sidebar by creating a second “page.php” whithout the <?php get_sidebar(); ?> assigned to the pages I don’t want to display plugins, but I don’t manage to set these 3 pages to maximum width… I tried changing width with page-id in the css as I saw on the forum, but I did not manage to change it and I’m not sure how to do it…

Here is my website: http://www.coloril.fr
The pages I would like to set full-width:
http://www.coloril.fr/galeries/broderie/
http://www.coloril.fr/galeries/serigraphie/

Thanks guys!