Examine source code of horizon-dark-rb9

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "horizon-dark",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "right top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(160, 224, 238, 0.25)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(0, 0, 0)",
      "tab_background_text": "rgb(255, 230, 217)",
      "toolbar_field": "rgb(0, 0, 0)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(255, 77, 120)",
      "popup": "rgb(8, 58, 90)",
      "popup_text": "rgb(255, 255, 255)",
      "button_background_hover": "rgba(255, 108, 143, 0.52)",
      "popup_highlight": "rgb(8, 58, 90)",
      "tab_selected": "rgb(167, 61, 87)",
      "tab_text": "rgb(255, 230, 217)",
      "tab_loading": "rgb(255, 77, 120)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b80ed8e3-5bc0-47cd-8801-e664747545dd}"
    }
  }
}