Examine source code of Blue blue soft :)

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Blue blue :)",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "right center"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(245, 255, 252, 0.1)",
      "toolbar_text": "rgb(3, 3, 31)",
      "frame": "rgb(226, 234, 215)",
      "tab_background_text": "rgb(0, 0, 0)",
      "toolbar_field": "rgba(255, 255, 255, 0)",
      "toolbar_field_text": "rgb(0, 0, 0)",
      "tab_line": "rgb(245, 255, 252)",
      "popup": "rgb(245, 255, 252)",
      "popup_text": "rgb(0, 0, 0)",
      "tab_loading": "rgb(245, 255, 252)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{25e5a54a-9feb-4515-8e10-60bd632d0ec4}"
    }
  }
}