Set the default border style to "solid"

[hanneslsm]

What problem does this address?

When adding the border properties in theme.json, I might not include "style": true. I'll get all the other elements in the UI, but they are useless, because no default border style is defined and no border will be shown.
"settings": { "border": { "color": true, "radius": true, "width": true },...

Even if I set the style to be true, I think the border style should have a default fallback, because the UI isn't that inutivelty showing me that I also have to click on one style to activate it.

What is your proposed solution?

Either add a default border style in Gutenberg or give the option to define a default in the theme.json.

[aaronrobertshaw]

This issue relates to the old border controls, which were updated in #37770. That PR also added additional default styles applying a solid border style to those added via #33743.

These defaults aren't bulletproof as it's still possible for blocks or themes to define border styles with a higher specificity however I believe they mostly achieve the proposed solution here.

Unfortunately, I don't think there is a way of determining when a block will have border color/width applied via theme.json or global styles CSS and then apply a default border style as well. In this scenario however, the theme author can still explicitly state the border style they are chasing.

	...
	"styles": {
		"blocks": {
			"core/group": {
				"border": {
					"color": "cyan",
					"width": "0.5em",
					"style": "solid"
				}
			}
		},
	}

While testing this I found a bug preventing the disabling/hiding of the border style control within the current border UI. A separate fix for that is up in #43109.

As this issue relates more specifically to "default" border styles, I'll close it for now.

Thanks for reporting this @hannesdev; please let me know if there are further tweaks we can make to the border support experience. 👍

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Click for demo of border support with style control disabled (using #43109)

Screen.Recording.2022-08-10.at.4.48.57.pm.mp4