It's dangerous to go alone, take this

body {
  /* https://systemfontstack.com/ */
  font-family: -apple-system, BlinkMacSystemFont, avenir next, avenir, segoe ui,
    helvetica neue, helvetica, Ubuntu, roboto, noto, arial, sans-serif;
  line-height: 1.5; /* basic readability */
  max-width: 70ch; /* 70 character max width */
  padding: 8px; /* padding for small screens (eg. mobile) */
  margin: 0 auto; /* center horizontally */
  color: #333; /* reduce constrast (optional?) */
}

a {
  color: #337ab7;
  text-decoration: none;
}
a:hover {
  text-decoration: underline;
}

Decisions

• According to this article 16px (the default) is the best font size. so I haven't changed it
• sans-serif instead of serif, according to this article sans-serif is slightly more readable

Other resources

• piccalil
• every-layout.dev
• lobotomized owls (not used, but interesting)