Examine source code of red-white gradation

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "red-white gradation",
  "manifest_version": 2,
  "description": "Gradation from red to white.\nSorry, if width=3000, it's gradation, but if shorter, it's almost red."
}