Adds basic CSS for readability to websites that lack it.
Sets max width, centers body and adds breathing room so that you don't have to turn or tilt your head to read.
Specifically:
document.body.style.maxWidth = "50em";
document.body.style.padding = "2em 0em";
document.body.style.margin = "0 auto";
document.body.style.lineHeight = "1.5";