3 column grid

You can make change in css for these.
Increase the width of site content artcle blogs.You can add these.

.blog .site-content .hentry,.archive .site-content .hentry,.search .site-content .hentry{width:393px;}

Hope these will help you..

Good CSS tip from Sprytechies!

A couple more things you might want to add to that are a height declaration so the images stay square, and a media query to limit the change to larger screens only, which will preserve the rest of the responsive CSS on smaller screens. For example, something like:

@media screen and (min-width: 1180px) {
   .blog .site-content .hentry, .archive .site-content .hentry, .search .site-content .hentry {
        width: 393px;
        height: 393px;
   }
}

p.s. it’s cool that you’re comfortable messing with the CSS, but don’t edit the theme files directly, otherwise your changes will be overwritten whenever the theme is updated. ??

An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS.

As alternatives, you could either install a standalone custom CSS plugin, or create a child theme.