A block style is a preset which holds a bundle of block attributes and their values, which you can apply to the currently selected block, by opening Block Settings → section "Styles" → clicking your desired style. E.g. for a button block the available styles in the Twenty Twenty Three theme are "Default" and "Outline".
Technical background information: A block style is a convenience function in the Block Editor GUI. You could achieve the same by going to the section "Advanced" and under "ADDITIONAL CSS CLASS(ES)" and add the corresponding classname, e.g. .is-style-outline for the "Outline" style.
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How will this new page help you?
If integrated in existing articles
I'd expect it here mostly:
This article documents how global styles work (which have their own side panel):
AFAIK I would describe a "Block Style" like this:
A block style is a preset which holds a bundle of block attributes and their values, which you can apply to the currently selected block, by opening Block Settings → section "Styles" → clicking your desired style. E.g. for a button block the available styles in the Twenty Twenty Three theme are "Default" and "Outline".
Technical background information: A block style is a convenience function in the Block Editor GUI. You could achieve the same by going to the section "Advanced" and under "ADDITIONAL CSS CLASS(ES)" and add the corresponding classname, e.g.
.is-style-outline
for the "Outline" style.The block style is defined in the theme's theme.json or the block's block.json