Examine source code of youtube-darked-theme

{
  "name": "youtube dark theme",
  "manifest_version": 2,
  "version": "1.0",
  "theme": {
    "images": {
      "theme_frame": "transparent_1x1.png"
    },
    "colors": {
      "frame": "rgba(40, 40, 40, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)",
      "toolbar": "rgba(70, 70, 70, 1)",
      "bookmark_text": "rgba(255, 255, 255, 1)",
      "toolbar_field": "rgba(40, 40, 40, 1)",
      "toolbar_field_text": "rgba(255, 255, 255, 1)",
      "tab_line": "rgba(40, 40, 40, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d980d957-168d-47fa-892f-433de6131445}"
    }
  }
}