Drop `hide-readme-header` feature #4157

That feature is great! Makes me wonder if we should drop collapse-markdown-sections instead.

I thought about it as well, but collapse-markdown-sections serves more purposes than a regular table of contents. For example you can take a screenshot with some sections folded to fit the content you want into a single screen.

Maybe pull the button out to the left of the readme (assuming the viewport is wide enough)?

<img width="400" alt="Screenshot_2021-03-26 13 27 24" src="https://user-images.githubusercontent.com/25517624/112670256-0f8a4f00-8e37-11eb-8c0a-d714cc898613.png"><img width="300" alt="Screenshot_2021-03-26 13 29 38" src="https://user-images.githubusercontent.com/25517624/112670489-55dfae00-8e37-11eb-9218-90aea51e9156.png">

Rough CSS:

#readme > :first-child {
  height: 0;
  padding: 0 !important;
  border: none !important;
}
#readme > :first-child details {
  position: absolute;
  left: -4em;
  top: 1em;
}

Alternatively, the space could be used to display the current header (or header breadcrumbs)

For example you can take a screenshot with some sections folded to fit the content you want into a single screen.

Sounds niche and I’m not convinced 🤔

Maybe pull the button out to the left of the readme

Doesn't seem worth the hassle and now the header is better than when the feature was introduced:

• 2 buttons
• white background
• fixed header

Maybe we could just reduce the padding to make it smaller:

padding: 4px 12px 4px 4px !important;

Just noticed the header title now points to #readme (I don't remember whether it's there before the table of contents), serving as a quick way to go to the top of the README.

Semi-related: I wonder why this issue still exists 🤔

EDIT: turns out this is caused by Refined GitHub, but I haven't figured out why.

Likely due to sticky-sidebar

The feature is expanded to all markup files. Sweet!

https://twitter.com/natfriedman/status/1382424314268372992

EDIT: :P never mind, guess everyone already knows it.