This is what I meant by the following:
Images in your theme are styled in such a way that they fill the space, aka
cover the available image space. You can change this application by setting them to
contain (like in the CSS I provided) however it’ll cause letterboxing to happen with images that don’t fit the aspect ratio.
Best thing to do is to create graphics with a decent amount of white space around them, or use feature images that aren’t hampered when they are cropped around the edges.
Hope this clears things up!