Example theme.json file

theme.json

{
  "version": 1,
  "settings": {
    "color": {
      "primary": "#0073aa",
      "secondary": "#005b8e",
      "text": "#333",
      "background": "#f5f5f5"
    },
    "typography": {
      "body": {
        "font-family": "Helvetica, Arial, sans-serif",
        "font-size": "16px",
        "line-height": "1.5",
        "letter-spacing": "0.5px"
      },
      "heading": {
        "font-family": "Georgia, serif",
        "font-weight": "bold",
        "letter-spacing": "-0.5px"
      }
    },
    "spacing": {
      "padding": "20px",
      "margin": "10px"
    },
    "layout": {
      "content-width": "700px"
    },
    "custom": {
      "my-custom-setting": "some value"
    }
  },
  "blocks": {
    "core/paragraph": {
      "color": {
        "text": "#666"
      },
      "typography": {
        "body": {
          "font-size": "18px"
        }
      }
    }
  }
}