Spacing

{
	"$schema": "https://schemas.wp.org/trunk/theme.json",
	"version": 2,
	"settings": {
		"spacing": {
			"spacingScale": {
				"operator": "+",
				"increment": 0.25,
				"steps": 7,
				"mediumStep": 1,
				"unit": "rem"
			}
		}
	}
}

Ressources : https://developer.wordpress.org/news/2023/03/everything-you-need-to-know-about-spacing-in-block-themes/#customizing-the-spacing-scale