When using styles: replicate the `classes` argument of `DataFrame.to_html`
Simple request:

The DataFrame `to_html` method accepted a kwarg `classes` to specify CSS classes that should be applied to the output HTML `<table>`.

When using the new(ish) DataFrame `.style` approach, as far as I can tell, no such option exists.  And it is not possible to work around this issue using the `.set_table_styles` approach, since my goal is to apply an existing bit of CSS to the table by giving  it a class (rather than re-specifying all the styles for this specific table).

Thoughts?