Examine source code of River Fog...

{
  "name": "River Fog...",
  "manifest_version": 2,
  "version": "4.0",
  "theme": {
    "images": {
      "theme_frame": "RiverFogH.jpg"
    },
    "colors": {
      "frame": "rgba(13, 13, 13, 0)",
      "tab_background_text": "rgba(214, 230, 255, 1)",
      "toolbar": "rgba(41, 40, 40, 0)",
      "bookmark_text": "rgba(213, 227, 250, 1)",
      "toolbar_field": "rgba(31, 30, 30, 0.1)",
      "toolbar_field_text": "rgba(212, 228, 255, 1)",
      "tab_line": "rgba(212, 228, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{69a726d7-fc89-456d-bee9-4c4f127acc60}"
    }
  }
}