Examine source code of Dark Mode Miku

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "miku",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "right top"
      ],
      "additional_backgrounds_tiling": [
        "no-repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(43, 42, 51)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(28, 27, 34)",
      "tab_background_text": "rgb(189, 189, 189)",
      "toolbar_field": "rgb(28, 27, 34)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(28, 96, 133)",
      "popup": "rgb(43, 42, 51)",
      "popup_text": "rgb(238, 238, 238)",
      "tab_loading": "rgb(28, 96, 133)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{19120b33-a9a9-4be6-add3-8dbb2c53becc}"
    }
  }
}