If you have the Stylish browser add-on (https://userstyles.org/), you can make this book much easier to read with this custom style I just wrote: “The Art of Unix Programming, and … Usability – improve readability”, https://userstyles.org/styles/107208/.
Here is the main part of the style’s CSS, if you just want to use your developer tools on each page:
body {
font-size: 20px;
line-height: 1.3;
max-width: 700px;
margin-left: auto;
margin-right: auto;
}
I referred to http://practicaltypography.com/summary-of-key-rules.html when choosing these numbers.