Examine source code of YouTube dark

{
  "manifest_version": 2,
  "version": "1.1",
  "name": "YouTube dark",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-000-5672c42860d5b06e1058dc477397f3ef.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(32, 32, 32)",
      "toolbar_text": "rgb(238, 238, 238)",
      "frame": "rgb(32, 32, 32)",
      "tab_background_text": "rgb(238, 238, 238)",
      "toolbar_field": "rgba(18, 18, 18, 0.95)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgba(62, 166, 255, 0.75)",
      "popup": "rgba(32, 32, 32, 0.97)",
      "popup_text": "rgb(238, 238, 238)",
      "button_background_active": "rgba(62, 166, 255, 0.75)",
      "button_background_hover": "rgba(255, 0, 0, 0.75)",
      "icons": "rgb(255, 255, 255)",
      "ntp_background": "rgb(32, 32, 32)",
      "ntp_text": "rgb(238, 238, 238)",
      "popup_border": "rgba(255, 0, 0, 0.75)",
      "sidebar_border": "rgba(62, 166, 255, 0.75)",
      "sidebar_text": "rgb(238, 238, 238)",
      "sidebar": "rgb(18, 18, 18)",
      "tab_selected": "rgb(18, 18, 18)",
      "tab_text": "rgb(255, 255, 255)",
      "toolbar_bottom_separator": "rgba(62, 166, 255, 0.75)",
      "toolbar_top_separator": "rgba(48, 48, 48, 0)",
      "tab_loading": "rgba(62, 166, 255, 0.75)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a8f8f88a-3ca4-4537-9fb3-1e60697dc9b6}"
    }
  }
}