I tried your code but nothing change, i’ve found the code which modify width (with the firefox inspector). You can see it on the attachment.
Could you please share me the page URL from your site where it is displaying so that i can help you?
I’m working on my computer with a local server so i can’t send you the link, if you can tell me which file manage this code, i probably could modify by myself if not i will be back when my site will be online.
Thank you everyone for your precious help !
This is CSS so you would have to check the style.css and the php templates which would be content-page.php and content.php
I hope this helps.