Examine source code of Proton Dark

{
  "manifest_version": 2,
  "version": "3.0",
  "name": "Proton Dark (Proton Ready)",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "dark.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(28, 28, 28)",
      "toolbar_text": "rgb(204, 204, 204)",
      "frame": "rgb(28, 28, 28)",
      "tab_background_text": "rgb(238, 238, 238)",
      "toolbar_field": "rgb(56, 56, 61)",
      "toolbar_field_text": "rgb(238, 238, 238)",
      "tab_line": "rgb(204, 204, 204)",
      "popup": "rgb(56, 56, 61)",
      "popup_text": "rgb(204, 204, 204)",
      "icons": "rgb(238, 238, 238)",
      "ntp_background": "rgb(28, 28, 28)",
      "ntp_text": "rgb(238, 238, 238)",
      "popup_border": "rgb(56, 56, 61)",
      "sidebar_border": "rgba(28, 28, 28, 0)",
      "sidebar_text": "rgb(238, 238, 238)",
      "sidebar": "rgb(28, 28, 28)",
      "tab_background_separator": "rgb(28, 28, 28)",
      "tab_loading": "rgb(28, 28, 28)",
      "tab_selected": "rgb(56, 56, 61)",
      "tab_text": "rgb(238, 238, 238)",
      "toolbar_bottom_separator": "rgb(28, 28, 28)",
      "toolbar_field_border_focus": "rgb(56, 56, 61)",
      "toolbar_field_border": "rgb(56, 56, 61)",
      "toolbar_field_separator": "rgb(56, 56, 61)",
      "toolbar_top_separator": "rgb(28, 28, 28)",
      "toolbar_vertical_separator": "rgb(28, 28, 28)"
    }
  }
}