Question:
Backgrou
.img-max {
max-width: 500px
}
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">
<p class="alert-primary p-3">
I can set the max-width of the image... but then it stops being responsive.
</p>
<div class="container">
<div class="img-max">
<img class=" mx-auto d-block mb-2 float-md-left mr-md-4 img-thumbnail" src="https://images.pexels.com/photos/2422/sky-earth-galaxy-universe.jpg">
</div>
<p>
Lorem ipsum dolor sit amet, consectetur adipisicing elit. Labore ipsa ea dolorem mollitia repudiandae odit dolore quod et voluptatem asperiores odio quam ipsam placeat nisi quo voluptate, laborum provident earum?
</p>
</div>
Your answer is here
.img-max {
max-width: 500px;
width:100%;
}
and use the class in the image.
I have edited your fiddle. Please refer the link
jsfiddle.net/saravanan7944/ygamjz7s/1