CSS:
spoiler to avoid clutter
*,
*:before,
*:after {
font-family: "Source Code Pro", "Noto Serif", serif;
}
:root {
font-size: 16px;
}
html {
background-color: #000;
max-width: 100vw;
}
body {
max-width: 60ch;
margin: 0 auto;
padding: min(10em, 10vw);
font-stretch: expanded;
background-color: rgb(238, 238, 216);
color: #333;
text-align: left;
}
p {
font-family: inherit;
text-align: inherit;
margin: 0;
margin-top: 1em;
margin-bottom: 1em;
}
p[class] {
font-family: inherit;
}
span.minor {
font-family: inherit;
}
h1,
h2,
h3,
h4,
h5,
h6 {
font-family: inherit;
}
a,
a:link,
a:visited {
color: #000;
text-decoration: underline dotted 2px;
}
img {
image-rendering: pixelated;
filter: grayscale(1);
}
img:hover {
image-rendering: initial;
filter: grayscale(0);
}
a:hover {
text-decoration: none;
background-color: black;
color: white;
}

The only thing that I don't like on marxists.org is the large paragraph width, though. This one looks a bit better for me (Font: Source Serif 4):
Pretty big waste of space with black bars, but it's nice for focus. I did think that the right side of the screenshot looked good.
(edited because I sounded pretentious)