I occasionally get (legal) texts send by customers. Usually exported in horrible HTML formatting via a WYSIWYG editor. I use the following style to make it look presentable, before I send it to our app developers.

<head>
    <style>
    body {
   font-family:sans-serif;
   line-height:140%;
   max-width:38rem;
   padding:2rem;
   margin:auto;
  }
  h1,h2,h3,h4,h5 {
   margin-bottom:.6rem;
   line-height:120%;
  }
  p {
   margin:0 0 1rem;
  }
    </style>
</head>

Additionally, I use the ‘replace’ functionality in my text editor to remove unnecessary divs, paragraphs and other elements.

If you are looking for a minimal way to make any HTML formatted page look good, here you go.