Add in-page right sidebar

[rrrrrrockpang]

Hello, thank you so much for the framework. I'd like to see whether I can put the in-page toc as a sidebar. For example, I can generate the toc below:

## Table of contents
{: .no_toc .text-delta }

1. TOC
{:toc}

However, I would love to put this toc on the right as people can easily navigate within my page. Something like the sidebar toc here: https://docs.github.com/en/get-started/quickstart/hello-world

[mattxwang]

Thanks for submitting an issue @rrrrrrockpang! I agree that this could be a very useful feature; #625 is a related issue (which targets a superset of this feature - also autogenerating it, etc.) that has some interest. Like I commented there, I'd be happy to review a PR that implements this, as long as it's opt-in and doesn't break backwards compatibility.

[bittlingmayer]

I would welcome this.

One problem with the GitHub implementation linked by @rrrrrrockpang is that it doesn't highlight as you scroll.

Here are some examples:

• https://substack.com/going-paid-guide#design

• https://a16z.com/16-things-to-know-about-the-409a-valuation/ (the progress bar across the top is also a nice touch).

[jonfroehlich]

FWIW, I did implement this myself a few years ago but used the external js lib tocbot. It would definitely be great to have this implemented natively.

Here's an example of the tocbot integration:

You can check it out here: https://makeabilitylab.github.io/physcomp/arduino/led-on.html.

Note that:

• The right sidebar doesn't pop-up until you scroll down the page
• The sections do highlight and auto-expand
• I never polished it to work well responsively (at all browser sizes)