How to reduce the site width

Link to a blog post: https://iamyoursidekik.com/best-foreign-films-on-netflix-right-now/

I’m using Blossom Coach theme and I wanna reduce my site’s width a little. As you can see the content of the site a very spread out. I wanna make the width as it’s in the demo. I don’t wanna remove the sidebar. Just wanna decrease the width a little. Anyone can help me do this??
Just see a blog post and you can see that the content looks so spread out.

The page I need help with: [log in to see the link]