Centering Main Menu & Posts

Hi! I love this theme, thank you for making it!

I wanted to adjust it so that, on the main, the sidebar is gone and the posts are centered on the full-width page. I’d also like to remove the social icons and have the main menu centered as well.

I was able to remove both the social icons and the sidebar but cannot get the menu or the posts centered on the page. Can you tell me what I can do to the CSS to change this? Thank you!