.site-content .post has `overflow: hidden;`, .site-content .entry-content has `max-width: 965px;`, and .wide-content has `margin-right: -34.0740%;` Disabling the margin-right or, preferably, the max-width rule will fix the layout. Or make your browser less than 1700px wide.

(Crazy rats nest of CSS rules, I assume this is a wordpress/wordpress template thing.)