Closes qunitjs#999
Fixes qunitjs#983

* Fix huge color contrast issue with the dark red background
  behind similarly dark colors, especially in `.counts`.

* Remove white padding between test item edge and assert list
  assertion green/red shading. Instead, add some border-spacing
  to the assert item table.

* Adjust various colors slightly to comply with WCAG guidelines.
  https://developer.mozilla.org/en-US/docs/Web/Accessibility/Understanding_WCAG/Perceivable/Color_contrast

* Fix broken `.qunit-test.pass .test-expected { color: qunitjs#999; }`
  override which was only applicable to passing "todo" tests as no
  other passing tests have failing assertions under them. This was
  meant to mute the colors of these failures to avoid distraction.
  However the CSS cascade has changed over time such that these
  styles no longer applied.

  This is likely masked by the fact that passing tests (including
  passing todos) are collapsed by default, so there's very little
  attention to these anyway.

  Restore these overrides, and extend them to the "diff" and
  "source" lines as well.

Easy way to identify color usage:

```
$ git grep '#[0-9A-F][0-9A-F]*' src/core/qunit.css | sed 's/^.*\(#[0-9A-F]*\).*/\1/' | sort | uniq -c
```

Ref qunitjs#1774.

* Fix huge color contrast issue with the dark red background
  behind similarly dark colors, especially in `.counts`.

* Remove white padding between test item edge and assert list
  assertion green/red shading. Instead, add some border-spacing
  to the assert item table.

* Adjust various colors slightly to comply with WCAG guidelines.
  https://developer.mozilla.org/en-US/docs/Web/Accessibility/Understanding_WCAG/Perceivable/Color_contrast

* Fix broken `.qunit-test.pass .test-expected { color: qunitjs#999; }`
  override which was only applicable to passing "todo" tests as no
  other passing tests have failing assertions under them. This was
  meant to mute the colors of these failures to avoid distraction.
  However the CSS cascade has changed over time such that these
  styles no longer applied.

  This is likely masked by the fact that passing tests (including
  passing todos) are collapsed by default, so there's very little
  attention to these anyway.

  Restore these overrides, and extend them to the "diff" and
  "source" lines as well.

Easy way to identify color usage:

```
$ git grep '#[0-9A-F][0-9A-F]*' src/core/qunit.css | sed 's/^.*\(#[0-9A-F]*\).*/\1/' | sort | uniq -c
```

Ref qunitjs#1774.

* Fix huge color contrast issue with the dark red background
  behind similarly dark colors, especially in `.counts`.

* Remove white padding between test item edge and assert list
  assertion green/red shading. Instead, add some border-spacing
  to the assert item table.

* Adjust various colors slightly to comply with WCAG guidelines.
  https://developer.mozilla.org/en-US/docs/Web/Accessibility/Understanding_WCAG/Perceivable/Color_contrast

* Fix broken `.qunit-test.pass .test-expected { color: #999; }`
  override which was only applicable to passing "todo" tests as no
  other passing tests have failing assertions under them. This was
  meant to mute the colors of these failures to avoid distraction.
  However the CSS cascade has changed over time such that these
  styles no longer applied.

  This is likely masked by the fact that passing tests (including
  passing todos) are collapsed by default, so there's very little
  attention to these anyway.

  Restore these overrides, and extend them to the "diff" and
  "source" lines as well.

Easy way to identify color usage:

```
$ git grep '#[0-9A-F][0-9A-F]*' src/core/qunit.css | sed 's/^.*\(#[0-9A-F]*\).*/\1/' | sort | uniq -c
```

Ref #1774.
Closes #1803.