A JavaScript error is thrown on running tests for ExtNet components in IE 11

[Dmitry-Ostashev]

Run the following test in IE 11 to reproduce the issue:

fixture `ExtNet`
    .page `https://examples3.ext.net/#/Form/Login/Auto_Complete`;

test('New Test', async t => {
    await t.debug();
});

You will see the following error:

  JavaScript error details:
  TypeError: Unable to get property 'cssText' of undefined or null reference
     at registerCssClass (https://speed.ext.net/ext.net/3.3.0/extnet/extnet-all.js:281:140)
     at Anonymous function (https://speed.ext.net/ext.net/3.3.0/extnet/extnet-all.js:2009:1)
     at Global code (https://speed.ext.net/ext.net/3.3.0/extnet/extnet-all.js:2006:2)

There is also an empty page in the browser.

This ExtNet example works properly in IE without TestCafe.

https://supportcenter.devexpress.com/internal/ticket/details/T1018570
https://github.com/DevExpress/testcafe-studio/issues/3926