To achieve a responsive behavior in a web site requires working with several HTML elements, images are one of the most requested. The are several techniques, the most simple one and with 99% backward compatibility (I'm looking to you IE 🤦‍♂️ ) is called Fluid Image, of course is not intended to solve all the problems, but it is a simple fix that works great most of the time.

            

img {
max-width: 100%;
height: auto;
}