Is it possible to make a blog full width instead of on the side?

Shopify Discussion
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3

Use custom css either for the blog templates in the theme editor or as a global theme CSS setting

https://help.shopify.com/en/manual/online-store/themes/theme-structure/extend/add-css

Try the following CSS

.article__inner { display: block; }

or to force it

.article__inner { display: block !important; }

Also be aware you color choices make the website hard to read with low contrast font-color on a near similar background color.