Hi Artin,
Your post page is set to contained width which removes the theme container paddings:
https://docs.generatepress.com/article/content-container/#contained
I checked wordsmith, it doesn’t have the same settings.
You can check 2 places:
1. If it happens to every post, then go to appearance > elements, check if there’s a layout element which set the content container to contained width:
https://docs.generatepress.com/article/layout-element-overview/#content-1
2. If not all the posts have this issue, go to the post which has this issue, in the post editor, check if you select the contained box in the layout metabox:
https://docs.generatepress.com/article/layout-metabox-overview/#where-is-it