editorial: revise custom stylesheets

[pkra]

Resolves #2226

• revise common.css
  • do we need any of it?
  • reduce css as per remove spec specific css or inline it #2226 (comment)
  • .image => remove after switching markup to figure
  • table styles (why does respec add borders in dark but not light mode?)
    • consider replacing our table styles with table.def from w3.org/StyleSheets/TR/2021/base.css (i.e., remove our custom styles and replace table classes with .def)
  • fix color contrast issues
    • color contrast issues speced/respec#4871
    • dark mode: th{ background-color:#eee; } (cf. Text-to-background contrast in tables under ARIA's Definition of Roles too low #2394 + duplicates)
    • syntax highlighting (light mode: IDL - dark mode: almost every code example)
      • specify a more accessible highlight.js palette
      • fix incorrect language detection such as #example-48 => https://github.com/speced/respec/wiki/ReSpec-Editor's-Guide#examples
  • ...
• revise core-aam.css
  • reduce css as per remove spec specific css or inline it #2226 (comment)
  • remove core-aam.css as they are covered via common.css
• pdf-aam: remove link to (now removed) core-aam.css
• accname styles
  • check remove spec specific css or inline it #2226 (comment) => less than reduced common.css for aria [the stylesheet has already been dropped]
• mapping-tables.css
  • ...
• editors.css - remove?
• slices.css - remove?
• html-aam.css - remove

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[pkra]

notes to self:

• the reduction of common.css in remove spec specific css or inline it #2226 (comment) includes more declarations than the reductions in remove spec specific css or inline it #2226 (comment) (core-aam) and remove spec specific css or inline it #2226 (comment) (accname). So we can start there.
• core-aam loads both core-aam.css and common.css so we can reduce core-aam.css further

[pkra]

It turns out, core-aam only sets styling that are already set in common.css.