Examine source code of Choco-

{
  "theme": {
    "images": {
      "theme_frame": "Choco-Header.png"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Choco-",
  "manifest_version": 2,
  "description": "Here's a delicious (I tasted it) variation of my Candied Hearts Persona.\nVisit the following URL to get toolbar buttons that compliments (better matches) this Persona.\n<a href=\"https://outgoing.prod.mozaws.net/v1/0f4c1ea5dde5c8c3fc33846f1f0d8ff1f6307e35d1ed5c46666c2e4d5e24013c/http%3A//www.accessfirefox.org/Hearts-Personas-for-Firefox.php\" rel=\"nofollow\">www.accessfirefox.org/Hearts-Personas-for-Firefox.php</a>\n\nThank you for shopping with us."
}