Examine source code of Dark Gray Custom

{
  "manifest_version": 2,
  "version": "1.2.1",
  "name": "Dark Gray Custom",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-000-5672c42860d5b06e1058dc477397f3ef.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(57, 57, 62)",
      "toolbar_text": "rgb(210, 214, 221)",
      "frame": "rgb(32, 33, 36)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(42, 43, 45)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(95, 111, 137)",
      "popup": "rgb(57, 57, 62)",
      "popup_text": "rgb(255, 255, 255)",
      "icons_attention": "rgb(101, 171, 248)",
      "popup_border": "rgb(84, 95, 116)",
      "popup_highlight": "rgb(82, 82, 92)",
      "toolbar_field_border_focus": "rgb(84, 95, 116)",
      "toolbar_field_highlight": "rgb(0, 120, 215)",
      "tab_loading": "rgb(95, 111, 137)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{08de0df4-411b-4729-8726-e731f29f4923}"
    }
  }
}