Examine source code of factorio theme 1

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#4f5441",
      "tab_background_text": "#c0c7db"
    }
  },
  "version": "2.0",
  "name": "factorio theme 1",
  "manifest_version": 2,
  "description": "Screenshots was taken from official Factorio site.\n<a rel=\"nofollow\" href=\"https://outgoing.prod.mozaws.net/v1/5b81bb73fb617869ac7948ea53e17a4dbf11fb182eb303967db950e91033b5a7/https%3A//www.factorio.com/screenshots\">https://www.factorio.com/screenshots</a>"
}