I want to apply
<img src="http://placehold.it/850x850" alt="App">
<div class="description">text you see in screenshot.
The max-width would have to be on the image.
Image elements don't care what dimensions their parent tells them--they will simply stretch the parent container to fit anyways.
Edit: for example, you can create a new rule whose selector is .screenshot img and then apply the max-width there.