Examine source code of Plum Gradient Darker

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Plum Custom Gradient",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "left top"
      ],
      "additional_backgrounds_tiling": [
        "repeat-y"
      ]
    },
    "colors": {
      "toolbar": "rgba(104, 95, 129)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(74, 65, 99)",
      "tab_background_text": "rgb(255, 255, 255)",
      "ntp_background": "rgb(0, 0, 0)",
      "ntp_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(222, 211, 206)",
      "toolbar_field_text": "rgb(0, 0, 0)",
      "tab_line": "rgb(0, 128, 128)",
      "popup": "rgb(222, 211, 206)",
      "popup_text": "rgb(0, 0, 0)",
      "button_background_active": "rgb(74, 65, 99)",
      "button_background_hover": "rgb(0, 128, 128)",
      "tab_loading": "rgb(205, 35, 185)",
      "tab_selected": "rgb(0, 128, 128)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8fc27705-8d2a-4a42-92b7-7da372cc705a}"
    }
  }
}