- Line height & font family from html were directly overridden by body, so they were redundant thus removed
- The remaining properties are moved to body
- Shim for IE10 tags removed
- hr cleanup
  - Combined styles from reboot & type
  - Changed from borders to background
    - This allows us to keep the color inherited.
    - Opacity can be used to change the intensity
    - Size attribute will not change the height instead of making the hr look like an input field
  - Better variable names
- headings cleanup
  - Moved all element styling to reboot
  - Type will now extend the element styling. This way we will save some redundant code
- small & mark are also moved to reboot. type does not contain any element styling anymore
- font weight removed from small, this did not really made sense

Removed leftover from #27789

Extrapolates the previously used selector into a new mixin that only generates valid CSS by creating psuedo-classes for `valid` and `invalid`, and nothing else.

Fixes #28380.

Currently, `$toast-border-radius` uses the value of `.25rem`. This is inconsistent with other variables such as `$btn-border-radius` and `$input-border-radius`, which uses the "global" `$border-radius` variable.

* Fix buttons :focus state styles

Buttons :hover and :focus state shares styles.
Buttons :focus text color on 'a.btn' is now consistent with others '.btn'.

* `:focus` styles should be in sync with `.focus`.

So shared styles with hover were copy to focus definition. Rather then using
`hover-focus` mixin which do not contain `.focus`.

We use only `https` for a few months now.