Examine source code of Watermill-3

{
  "manifest_version": 2,
  "version": "2.0",
  "name": "Watermill-3",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "right top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(255, 255, 255, 0)",
      "toolbar_text": "rgb(0, 0, 0)",
      "frame": "rgb(96, 98, 103)",
      "tab_background_text": "rgb(236, 237, 242)",
      "toolbar_field": "rgba(0, 0, 0, 0.3)",
      "toolbar_field_text": "rgb(236, 237, 242)",
      "tab_line": "rgba(255, 255, 255, 0.15)",
      "popup": "rgb(82, 83, 87)",
      "popup_text": "rgb(255, 255, 255)",
      "button_background_active": "rgba(0, 0, 0, 0.25)",
      "button_background_hover": "rgba(0, 0, 0, 0.15)",
      "icons_attention": "rgb(236, 237, 242)",
      "icons": "rgb(236, 237, 242)",
      "ntp_text": "rgb(236, 237, 242)",
      "popup_border": "rgba(255, 255, 255, 0.3)",
      "popup_highlight_text": "rgb(0, 0, 0)",
      "popup_highlight": "rgba(139, 143, 149, 0.9)",
      "sidebar_border": "rgba(255, 255, 255, 0.3)",
      "sidebar_highlight_text": "rgb(0, 0, 0)",
      "sidebar_highlight": "rgba(139, 143, 149, 0.9)",
      "sidebar_text": "rgb(255, 255, 255)",
      "sidebar": "rgb(96, 98, 103)",
      "tab_background_separator": "rgba(0, 0, 0, 0)",
      "tab_loading": "rgb(255, 255, 255)",
      "tab_selected": "rgba(0, 0, 0, 0.3)",
      "tab_text": "rgb(255, 255, 255)",
      "toolbar_bottom_separator": "rgb(82, 83, 87)",
      "toolbar_field_border_focus": "rgba(255, 255, 255, 0.15)",
      "toolbar_field_border": "rgba(255, 255, 255, 0.3)",
      "toolbar_field_focus": "rgba(96, 98, 103, 0.9)",
      "toolbar_field_highlight_text": "rgb(0, 0, 0)",
      "toolbar_field_highlight": "rgba(139, 143, 149, 0.9)",
      "toolbar_top_separator": "rgba(255, 255, 255, 0)",
      "toolbar_vertical_separator": "rgb(236, 237, 242)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{44ef7965-6950-4058-a5b5-ba84f7347288}"
    }
  }
}