Examine source code of Developer Theme

{
  "name": "Developer Theme",
  "manifest_version": 2,
  "version": "1.0",
  "theme": {
    "images": {
      "theme_frame": "5557995.jpg"
    },
    "colors": {
      "frame": "rgba(5, 31, 92, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{cea12e5e-019c-49c5-b316-29a76549ff11}"
    }
  }
}