Image block: Add font size control for captions

[scruffian]

What problem does this address?

Themes need a way to control font size of captions for image blocks.

What is your proposed solution?

We could add a control for font size to the block and have it target captions with experimentalSelector. Alternatively we could add support for figcaption to the elements part of Global Styles.

[glendaviesnz]

Changed the title to Image block as once experimental flag removed for refactored gallery the gallery images are Images blocks - so fix should primarily target the Image block. Switch it back @scruffian if I have misunderstood this.

[ramonjd]

Just adding some cursory experimental findings.

I added typography block support to the Image block and gave the <figcaption /> a style of font-style: inherit, overriding the currently-defined 13px.

Works fine, albeit the default figcaption font size inherits from up the tree somewhere, in the example below, from --wp--preset--font-size--normal so it's slightly bigger.

The 13px, I discovered, comes from a mixin that adds default styles to captions for Audio, Embed, Table and Video Blocks, under the assumption that "figcaptions are not likely to be styled in the majority of existing themes". Example

So to keep the status quo we'd need to ensure that the 13px from the mixin is the default until a user-defined font value is detected.

I'm not so sure that typography support on the Image block is even appropriate. Perhaps we could had something to the block inspector toolbar?

[beafialho]

+1 this would be really useful! In addition, it would be great to be able to edit the alignment of the caption to be center, left and right aligned.

[richtabor]

Alternatively we could add support for figcaption to the elements part of Global Styles.

@scruffian Think this is good to close, now that we have captions in Global Styles via #34643?

[scruffian]

Happy to close this for now. If we feel like we need per-block control we can open another issue.