Examine source code of Proton Slate

{
  "manifest_version": 2,
  "name": "Proton Slate",
  "description": "A Proton slate color scheme with improved contrast.",
  "author": "Zeke Farwell",
  "version": "1",
  "icons": {
    "32": "icon.svg"
  },
  "theme": {
    "colors": {
      "tab_background_text": "rgb(0,0,0)",
      "tab_selected": "rgba(255, 255, 255, 0.4)",
      "tab_text": "rgb(0,0,0)",
      "icons": "rgb(0, 0, 0)",
      "frame": "rgb(90, 105, 125)",
      "frame_inactive": "rgb(140, 155, 175)",
      "popup": "#fff",
      "popup_text": "rgb(21,20,26)",
      "popup_border": "transparent",
      "popup_highlight": "#e0e0e6",
      "popup_highlight_text": "#15141a",
      "tab_line": "transparent",
      "toolbar": "rgba(255, 255, 255, 0.8)",
      "toolbar_top_separator": "rgba(255, 255, 255, 0.9)",
      "toolbar_bottom_separator": "rgb(160, 164, 170)",
      "toolbar_field": "rgb(255, 255, 255)",
      "toolbar_field_text": "rgb(21,20,26)",
      "toolbar_field_border": "rgb(170, 174, 180)",
      "toolbar_field_focus": "rgb(255, 255, 255)",
      "toolbar_text": "rgb(0,0,0)",
      "ntp_background": "#F9F9FA",
      "ntp_text": "rgb(12, 12, 13)",
      "popup_action_color": "rgb(21,20,26)",
      "button": "rgb(240,240,244)",
      "button_hover": "rgb(224,224,230)",
      "button_active": "rgb(207,207,216)",
      "panel_hover": "rgb(224,224,230)",
      "panel_active": "rgb(207,207,21)",
      "panel_active_darker": "rgb(191,191,201)",
      "urlbar_result_hover": "rgb(240,240,244)"
    },
    "properties": {
      "panel_hover": "color-mix(in srgb, currentColor 12%, transparent)",
      "panel_active": "color-mix(in srgb, currentColor 20%, transparent)",
      "panel_active_darker": "color-mix(in srgb, currentColor 27%, transparent)"
    }
  }
}