Change helperto safeHTMLElement now that appElement is gone

src/components/Modal.js

@@ -3,7 +3,7 @@ import ReactDOM from 'react-dom';
 import PropTypes from 'prop-types';
 import ModalPortal from './ModalPortal';
 import * as ariaAppHider from '../helpers/ariaAppHider';
-import { AppElement, SafeHTMLElement } from '../helpers/appElement';
+import SafeHTMLElement from '../helpers/safeHTMLElement';
 
 export const portalClassName = 'ReactModalPortal';
 export const bodyOpenClassName = 'ReactModal__Body--open';

src/components/ModalPortal.js

@@ -5,7 +5,7 @@ import * as focusManager from '../helpers/focusManager';
 import scopeTab from '../helpers/scopeTab';
 import * as ariaAppHider from '../helpers/ariaAppHider';
 import * as refCount from '../helpers/refCount';
-import { SafeHTMLElement } from '../helpers/appElement';
+import SafeHTMLElement from '../helpers/safeHTMLElement';
 
 // so that our CSS is statically analyzable
 const CLASS_NAMES = {

src/helpers/safeHTMLElement.js

@@ -0,0 +1,7 @@
+import ExecutionEnvironment from 'exenv';
+
+const EE = ExecutionEnvironment;
+
+const SafeHTMLElement = EE.canUseDOM ? window.HTMLElement : {};
+
+export default SafeHTMLElement;