How to automatically adjust picture size to screen size

This is my dad's website: www.tremsky.com

He is wondering if there is a way to make all the pictures on all the pages, to automatically fit to screen size, independent of which screen it is.

I found this after doing some research:

<style>
   * {
       margin: 0;
       padding: 0;
   }
   .imgbox {
       display: grid;
       height: 100%;
   }
   .center-fit {
       max-width: 100%;
       max-height: 100vh;
       margin: auto;
   }
</style>



<img class="center-fit" src='pic.png'>

Would that help in any way? And how would I go about using it?