Examine source code of Heat Gradient

{
  "manifest_version": 2,
  "version": "1.2",
  "name": "Heat Gradient",
  "theme": {
    "colors": {
      "frame": "black",
      "frame_inactive": "#ffffff29",
      "icons_attention": "white",
      "icons": "white",
      "bookmark_text": "white",
      "tab_background_text": "white",
      "tab_text": "white",
      "tab_selected": "#ffffff29",
      "tab_line": "transparent",
      "tab_background_separator": "transparent",
      "toolbar": "transparent",
      "toolbar_field_highlight": "#ffffff4f",
      "toolbar_field_highlight_text": "white",
      "toolbar_field": "rgba(0, 0, 0, 0.32)",
      "toolbar_field_border": "#373737",
      "toolbar_field_border_focus": "rgb(68, 68, 68)",
      "toolbar_field_focus": "rgb(68, 68, 68)",
      "toolbar_field_text": "white",
      "toolbar_bottom_separator": "black",
      "toolbar_top_separator": "transparent",
      "toolbar_vertical_separator": "black",
      "toolbar_field_separator": "black",
      "popup": "rgba(0, 0, 0, 0.75)",
      "popup_text": "white",
      "popup_border": "black",
      "popup_highlight": "black",
      "popup_highlight_text": "red",
      "sidebar": "black",
      "sidebar_highlight": "red",
      "sidebar_highlight_text": "white",
      "sidebar_text": "white",
      "sidebar_border": "transparent"
    },
    "images": {
      "theme_frame": "background.svg"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{463c5d97-2224-41de-98a3-6b0b51fcda7a}"
    }
  }
}