RFR: [Updated] Update tables in java.base to be HTML5-friendly.

[Martin Buchholz]

Looks good.

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I suspect there's some way to specify the styles more compactly, but I
don't know enough css to say.

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+table.borderless thead tr th, table.borderless tbody tr th,
table.borderless tr th,

+table.plain > thead > tr > th, table.plain > tbody > tr > th, table.plain
> tr > th,

I was surprised at the difference in syntax; why the ">" in one but not the
other?