Tweaking CSS to make object docs more legible.

[yusuf-goog]

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[yusuf-goog]

Tweaking docs so that properties/methods/operators are slightly more legible.

Current style (e.g. https://api.flutter.dev/flutter/widgets/AbsorbPointer-class.html):

to new style:

[Hixie]

test-exempt: configuration change

cc @gspencergoog

[gspencergoog]