Theme: Twentythirteen – featured image does not resize well on mobile screen

Hi All,

I have this new site, https://www.vistaeconomica.com/, and the mobile version was working pretty well (resizing, etc.) until I published a post with a featured image. Now the mobile site does not property re-size the screen (words too small, featured image larger than it should be). Suggestions on how to fix this is very appreciated. New to WP here.

Thanks!