Windows XP

Looks like Windows XP.

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manifest.json

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Windows xp",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.jpg",
        "images/1.jpg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "center bottom",
        "right top"
      ],
      "additional_backgrounds_tiling": [
        "no-repeat",
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(0, 85, 227)",
      "toolbar_text": "rgb(0, 0, 0)",
      "frame": "rgb(0, 85, 227)",
      "tab_background_text": "rgb(251, 251, 250)",
      "toolbar_field": "rgb(251, 251, 250)",
      "toolbar_field_text": "rgb(0, 0, 0)",
      "tab_line": "rgb(226, 184, 16)",
      "popup": "rgb(251, 251, 250)",
      "popup_text": "rgb(0, 0, 0)",
      "tab_loading": "rgb(226, 184, 16)"
    }
  }
}