I wrote my version here last year: https://www.swyx.io/css-100-bytes

    html {
      max-width: 70ch;
      padding: 3em 1em;
      margin: auto;
      line-height: 1.75;
      font-size: 1.25em;
    }

if you have 100 more to spare:

    h1,h2,h3,h4,h5,h6 {
      margin: 3em 0 1em;
    }

    p,ul,ol {
      margin-bottom: 2em;
      color: #1d1d1d;
      font-family: sans-serif;
    }

explanation in the blogpost