title: addCssFile() no longer functions in our app. Is not called and does nothing
body: <p>Our app is no longer able to use the tns core function addCssFile().  The function is not called at all.  </p>
  
  <p>I tried altering one of the addCssFile() calls by calling a made up filename.  It does not trigger any errors and the code seems to skip right over it.  We made no changes to this script but suddenly this function does absolutely nothing.</p>
  
  <p>I added the import addCssFile portion to the code just now, and it says "module has no exported member"</p>
  
  <pre><code>  import * as applicationSettings from 'tns-core-modules/application-settings';
    import { localize } from 'nativescript-localize';
    import { ToastDuration, Toasty } from 'nativescript-toasty';
    import { fromObject } from 'tns-core-modules/data/observable';
    import { Page, topmost } from 'tns-core-modules/ui/frame';
    import {addCssFile} from 'tns-core-modules/ui/core/view';
  
    const source = fromObject({});
  
    source.set('settingsItems', [
      { name: localize('ColorSchemeMenu.ob'), enabled: true },
      { name: localize('ColorSchemeMenu.bw'), enabled: true },
      { name: localize('ColorSchemeMenu.rw'), enabled: true },
      { name: localize('ColorSchemeMenu.py'), enabled: true }
    ]);
  
    export function onNavigatingTo(args: any) {
      const page = args.object;
      page.bindingContext = source;
    }
  
    export function settingsItemTapped(args: any) {
      const button = args.object;
      const homePage = button.page.navigationContext.homePage as Page;
      const currentTheme = applicationSettings.getString('theme', 'blue');
  
      if (button.text === localize('ColorSchemeMenu.ob')) {
        //Orange
        homePage.addCssFile('themes/orange.css');
        applicationSettings.setString('theme', 'orange');
      } else if (button.text === localize('ColorSchemeMenu.bw')) {
        // Blue
        homePage.addCssFile('themes/blue.css');
        applicationSettings.setString('theme', 'blue');
      } else if (button.text === localize('ColorSchemeMenu.rw')) {
        // Red
        homePage.addCssFile('themes/red.css');
        applicationSettings.setString('theme', 'red');
      } else if (button.text === localize('ColorSchemeMenu.py')) {
        // Purple
        //homePage.addCssFile('themes/purple.css');
        homePage.addCssFile('themes/needstofail.css');
        applicationSettings.setString('theme', 'purple');
      }
  
      console.log('\n\ncolor scheme has been set to: ', applicationSettings.getString('theme'), '\n\n');
      new Toasty(
        `${localize('ColorSchemeMenu.changedMsg')} ${button.text}`,
        ToastDuration.SHORT
      ).show();
  
      //transition back to settings page after selecting color scheme
      topmost().navigate({
        moduleName: 'home/home-page',
        animated: true,
        transition: {
          name: 'slideRight'
        }
      });
  
    }
  
  
    export function homeBtnTapped(args: any) {
      topmost().navigate({
        moduleName: 'home/home-page',
        animated: true,
        transition: {
          name: 'slideRight'
        }
      });
    }
  </code></pre>
  
  <p>Clicking any of the buttons on the settings page should add the css info to the home page and alter the object colors.  The app recognizes that the buttons are pressed, but no css changes occur.  Manually changing the css file of the home page does alter the appearance of the page.</p>