nixpkgs/doc/overrides.css

.docbook .xref img[src^=images\/callouts\/],
.screen img,
.programlisting img,
.literallayout img,
.synopsis img {
    width: 1em;
}

.calloutlist img {
    width: 1.5em;
}

.prompt,
.screen img,
.programlisting img,
.literallayout img,
.synopsis img {
    -moz-user-select: none;
    -webkit-user-select: none;
    -ms-user-select: none;
    user-select: none;
}