This adds dynamic navigation of headers of the current page in the
sidebar. This is intended to help the user see what is on the current
page, and to be able to more easily navigate it. The "current" header is
tracked based on the scrolling behavior of the user, and is marked with
a small circle. This includes automatic folding to help keep it from
being too unwieldy on a page with a lot of nested headers.
This includes the `output.html.sidebar-header-nav` option to disable it.
I'm sure there are tweaks, fixes, and improvements that can be made. I'd
like to get this out now, and iterate on it over time to make
improvements.
Nim is a systems programming language (included in the highlight.js
`system` group), and we're quite happily using `mdBook` in several of
our documentation projects starting with our [style
guide](https://status-im.github.io/nim-style-guide/).
While we can maintain our own highlight.js, including `Nim` in the
default distribution would allow us to promote more mdBook usage in the
Nim community at the cost of a ~2kb increase in the `highlight.js` size.
Allows for special styles to call them out since they're different than
normal text and different than code. They can make use of styles they
inherit for font style and weight.
Notes on changes:
- Added new CSS variables for reused elements
- The font-* rules are separate for each aspect so that they can inherit
bold/italic/etc
Closes https://github.com/rust-lang/mdBook/issues/1813
