Examine source code of Adwaita Dark (GTK4)

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Adwaita Dark (GTK4)",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-008-60d2718f8c915b5ba09f31df5555b459.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(48, 48, 48)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(31, 31, 31)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(68, 68, 68)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(68, 68, 68)",
      "popup": "rgb(48, 48, 48)",
      "popup_text": "rgb(255, 255, 255)",
      "icons": "rgb(255, 255, 255)",
      "ntp_background": "rgb(31, 31, 31)",
      "ntp_text": "rgb(255, 255, 255)",
      "tab_loading": "rgb(68, 68, 68)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{0f130809-3203-4ef4-885d-e5d1da906bbb}"
    }
  }
}