Can I change the width of the sidebar for blog?

I’ve set my home page to display the latest blog posts. I’d like to show the sidebar, but it takes up too much real estate on the side. I have the masonry grid set up to show 2 columns (and I’ve selected full-width page in the general options)…and it looks like the 2 blog columns are 1/3rd of the screen each, and the sidebar is also 1/3rd. Ideally I’d like to have the 2 blog columns be 80% of the page total, and the sidebar be the other 20%. Any way to change that?