Examine source code of SierraOS background blur

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#424242"
    }
  },
  "version": "2.0",
  "name": "SierraOS background blur",
  "manifest_version": 2,
  "description": "This is a theme based on the original background and theme of macOS Sierra. It's light and gives a nice integrated look to the apple systems."
}