Examine source code of Plain Dark

{
  "name": "Plain Dark",
  "manifest_version": 2,
  "version": "1.0",
  "theme": {
    "images": {
      "theme_frame": "Transparent.png"
    },
    "colors": {
      "frame": "rgba(26, 26, 26, 1)",
      "tab_background_text": "rgba(153, 153, 153, 1)",
      "toolbar": "rgba(71, 71, 71, 1)",
      "bookmark_text": "rgba(240, 240, 240, 1)",
      "toolbar_field": "rgba(97, 97, 97, 1)",
      "toolbar_field_text": "rgba(235, 235, 235, 1)"
    }
  }
}