Problem:  Other than `state()` these are widely supported CSS features
Solution: Add :host, :host-context(), slotted(), and state() CSS
          pseudo-classes and functions (S0AndS0).

Reference:
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Selectors/:host
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Selectors/:host_function
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Selectors/::slotted
- https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Selectors/:state

TLDR: `host` and `host-context()` are useful for shadowDom stuff,
`::slotted()` enables targeting elements passed/injected into a
`<template>` and `state()` enables targeting custom identifiers.

For example, currently I'm (ab)using `:host` as a drop-in replacement
for `:root` when defining variables that are intended to be shared
across custom/template elements;

- `./assets/css/host.css`
   ```css
   :host {
     --default__margin-block: 0.25rem;
   }
   ```
- `./custom-elements/example.html`
   ```html
   <template>
     <link rel="stylesheet" href="/assets/css/host.css">

     <style>
       header {
         margin-block-start: calc(var(--default__margin-block) * 2);
       }
     </style>

     <header></header>
   </template>
   ```

closes: vim/vim#21404

https://github.com/vim/vim/commit/43725acce680d1b999e22fad68cea99c2b593325

Co-authored-by: S0AndS0 <strangerthanbland@gmail.com>

This is defined in the 'CSS Overflow Module Level 3' spec[1] and
supported by recent versions of all browsers reported by MDN[2], see the
MDN page also for the available values.

Link: https://drafts.csswg.org/css-overflow/#scrollbar-gutter-property [1]
Link: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/scrollbar-gutter#browser_compatibility [2]

related: vim/vim#20639
closes:  vim/vim#20653

https://github.com/vim/vim/commit/06512b153cd8b432bb24087143299f082a353885

Co-authored-by: Jay Sitter <jay@jaysitter.com>
Co-Authored-by: Matthew Hughes <matthewhughes934@gmail.com>

- Add missing numeric units to css syntax script
  (baseline 2015, 2020, 2022, 2023, 2026):
    dvb, dvh, dvi, dvmax, dvmin, dvw ic,
    lvb, lvh, lvi, lvmax, lvmin, lvw, svb, svh,
    svi, svmax, svmin, svw, vb, vi, x, cap, lh,
    rlh, rcap, rch, rex, ric

closes: vim/vim#19325

https://github.com/vim/vim/commit/1cf38bfebeeb322a8437a7c1fd12506661bbfa82

Co-authored-by: DuckAfire <155199080+duckafire@users.noreply.github.com>

This reverts commits:
- 6b652a785033fd4164e049492a7327c1ed7c3e5f
- 2f689d5abde0ccddca9e20d8c93a0299bd054e32
- a025a46d4169587145fb54f04af349cd05cb6122

Several email addresses that are known to be valid caused bounces
due to an issue with my email setup. The previous commits incorrectly
marked these addresses as invalid. So revert the whole thing again.

https://github.com/vim/vim/commit/62d8f3dab5a0b30c31a8df86a973c5e59821a3f0

N/A patch:
vim-patch:2f689d5: runtime: mark more invalid email addresses

Co-authored-by: Christian Brabandt <cb@256bit.org>

https://github.com/vim/vim/commit/2f689d5abde0ccddca9e20d8c93a0299bd054e32

Skip colors/ and syntax/help_ru.vim: missing previous changes.

Co-authored-by: Christian Brabandt <cb@256bit.org>

closes: vim/vim#18717

https://github.com/vim/vim/commit/f85951fee0e3ccd48ccfaeec9c09f96e325925d1

Co-authored-by: Neil Lambert <nlambert@pm.me>

runtime(css): update syntax script

https://github.com/vim/vim/commit/e84490311ba32cb258cc738bc3caa8b448c84c8b

Co-authored-by: Jay Sitter <jay@jaysitter.com>

runtime(css): Update pseudo-classes in syntax script (vim/vim#11595)

https://github.com/vim/vim/commit/309ded19543c140375b28ef562257e9f22c918c6

Co-authored-by: Adrian Heine né Lang <mail@adrianheine.de>

Update runtime files
https://github.com/vim/vim/commit/0e6adf8a29d5c2c96c42cc7157f71bf22c2ad471

Update runtime files
https://github.com/vim/vim/commit/2286304cdbba53ceb52b3ba2ba4a521b0a2f8d0f