Examine source code of Horizon

{
  "manifest_version": 2,
  "version": "1.1",
  "name": "Horizon",
  "theme": {
    "colors": {
      "toolbar": "rgb(55, 57, 74)",
      "toolbar_text": "rgb(213, 216, 218)",
      "frame": "rgb(28, 30, 38)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(46, 48, 62)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgba(103, 150, 230, 0)",
      "popup": "rgb(46, 48, 62)",
      "popup_text": "rgb(213, 216, 218)",
      "icons_attention": "rgba(103, 150, 230, 0.8)",
      "ntp_background": "rgb(28, 30, 38)",
      "sidebar_border": "rgb(46, 48, 62)",
      "sidebar_highlight": "rgb(55, 57, 74)",
      "sidebar_text": "rgb(213, 216, 218)",
      "sidebar": "rgb(46, 48, 62)",
      "toolbar_field_border_focus": "rgba(103, 150, 230, 0.8)",
      "toolbar_top_separator": "rgba(0, 0, 0, 0)",
      "tab_loading": "rgba(103, 150, 230, 0)"
    }
  }
}