* Update buttons.md
Updates the buttons documentation to refer to the button styles as variants as opposed to "predefined styles" as that language was previously troublesome elsewhere in our docs, and variants makes more sense.
* Update site/content/docs/5.3/components/buttons.md
Co-authored-by: Julien Déramond <julien.deramond@orange.com>
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Co-authored-by: Julien Déramond <julien.deramond@orange.com>
* Docs: add explanation of the base `.btn` class
and a callout reminding authors to at least define some focus styling if they intend to use it "naked"
* Turn callout into a warning
* Add initial heading
* Tweak callout wording