Align to CSS coding guidelines and fix CSSLint errors & warnings

Align to CSS coding guidelines and fix CSSLint errors & warnings

Fixes included are:
- Coding guidelines: align colors
- Coding guidelines: put every selector of combined selectors on
one line
- Coding guidelines: use `border: 0` instead of `border: none`
and put border shortcut structure into same order across selectors
for better gzipping
- Coding guidelines: whitespace in parenthesis
- CSSLint: disable applying `margin` for inline elements
- General: clean-up comments
- General: join pagination and 'Generic HTML elements'' rules
- General: add `word-wrap: break-word` to `pre, .mw-code` selector
to aggressively wrap long words
- General: swap `1px` border values with `1pt`
- General: integrate `word-wrap: break-word` on `.external` links
with possible overlong URLs
- General: do the `list-style` shorthand property right.

Bug: T120154
Change-Id: I29bf055e2b4fc0e26ce84243f6b612b4a6214b02