Mailspring/app/internal_packages/screenshot-mode/lib/main.es6

import fs from 'fs';
import path from 'path';

let style = null;

export function activate() {
  return AppEnv.commands.add(document.body, 'window:toggle-screenshot-mode', () => {
    if (!style) {
      style = document.createElement('style');
      style.innerText = fs
        .readFileSync(path.join(__dirname, '..', 'assets', 'font-override.css'))
        .toString();
    }

    if (style.parentElement) {
      document.body.removeChild(style);
    } else {
      document.body.appendChild(style);
    }
  });
}

export function deactivate() {
  if (style && style.parentElement) {
    return document.body.removeChild(style);
  }
}