Grey bars on the sides

I am new to wordpress but I managed to install it on my website and also embedded with the rest of the site. I started using the default theme but removed most of the colours and images. The only thing that I still haven’t manage to remove are 2 shaded grey bars on the sides of the page. I looked everywhere in the css and other pages and haven’t managed to find the relevant code. I’m sure this is straightforward but I would appreciate if anyone could help me.
This is how the page looks at the moment:

https://www.forceofthestreet.com/blog/

Thank you!