Responsive mode doesn't scale images – page is narrow

My website: https://www.allianceabroad.com has a responsive theme that is not properly scaling images and leaves pages narrow and left justified. Check it out on mobile to see what I am talking about. This site is using the AIT theme Guesthouse and I have tried to insert several different CSS codes into the custom CSS section of the theme.

Tried: img {max-width:100%}

Tried: <?php if(has_post_thumbnail()) { $image_src = wp_get_attachment_image_src( get_post_thumbnail_id(),’thumbname’ ); echo ‘<img src=”‘ . $image_src[0] . ‘” width=”100%” />’; } ?>

and a few others with no luck. Also added <div class=”video-container”></div> to videos, which helped on another site I manage with a different theme.

Any solutions?

Thanks.