Using
#lang scribble/base
produces HTML output in the old style, while
#lang scribble/manual
uses the new style.
To get the new style without switching to `#lang scribble/manual`,
use `manual-doc-style`.
Related changes include the addition of `css-style-addition` and
`js-style-addition`.
original commit: b520b66c4e8e54909c7d7b1126044e984989e8ef