Examine source code of Soft Grey

{
  "theme": {
    "images": {
      "theme_frame": "persona-header-gradient-white_grey.png"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#3d3c3c"
    }
  },
  "version": "2.0",
  "name": "Soft Grey",
  "manifest_version": 2,
  "description": "The is a soft white to grey gradient that gives the browser an easy-on-the-eyes look."
}