Examine source code of Developer Theme

{
  "name": "Developer Theme",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "theme.png"
    },
    "colors": {
      "toolbar": "rgba(166, 176, 230, 1)",
      "toolbar_field": "rgba(255, 102, 102, 1)",
      "toolbar_field_text": "rgba(255, 255, 255, 1)",
      "frame": "rgba(0, 81, 255, 1)",
      "tab_background_text": "rgba(255, 0, 0, 1)",
      "bookmark_text": "rgba(255, 255, 255, 1)"
    }
  }
}