From swyix.io who in turn cites HN’s @JoshuaRLi as a source, a small snippet of CSS to begin any style with:
html {
max-width: 70ch;
padding: 3em 1em;
margin: auto;
line-height: 1.75;
font-size: 1.25em;
}
This adds a nice space between lines, uses a readable font size, and guarantees some margin on the sides of the page, while giving enough space for text.