Examine source code of The theme I use

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "a nice pink theme",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-012-1e971c5fbb8dec3acbd76dd6c6819de9.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(255, 237, 255, 0.65)",
      "toolbar_text": "rgb(0, 0, 0)",
      "frame": "rgb(255, 179, 201)",
      "tab_background_text": "rgb(77, 58, 58)",
      "toolbar_field": "rgba(102, 102, 102, 0.22)",
      "toolbar_field_text": "rgb(0, 0, 0)",
      "tab_line": "rgba(255, 255, 255, 0)",
      "popup": "rgb(255, 255, 255)",
      "popup_text": "rgb(0, 0, 0)",
      "ntp_background": "rgb(252, 198, 228)",
      "tab_loading": "rgba(255, 255, 255, 0)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{edf5da2f-3a0c-4a3e-a52c-1f19a5cde143}"
    }
  }
}