Global Margins in Block Theme

Heading

{
  "version": 2,
  "settings": {
    "spacing": {
      "margin": true,
      "padding": true
    }
  },
  ...
  "styles": {
    "elements": {
      "h2": {
        "spacing": {
          "margin": {
            "bottom": "30px"
          }
        }
      }
    }
  }
}

Paragraph

"blocks": {
      "core/paragraph": {
        "spacing": {
          "margin": {
            "bottom": "20px"
          }
        }
      }
    }