Examine source code of basic dark theme

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#374048",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "basic dark theme",
  "manifest_version": 2
}