Adding hard-coded application header.

src/courseware/sequence/Unit.jsx

@@ -0,0 +1,22 @@
+import React, { useRef } from 'react';
+import PropTypes from 'prop-types';
+import { getConfig } from '@edx/frontend-platform';
+
+export default function Unit({ id, pageTitle }) {
+  const iframeRef = useRef(null);
+  const iframeUrl = `${getConfig().LMS_BASE_URL}/xblock/${id}`;
+
+  return (
+    <iframe
+      className="flex-grow-1"
+      title={pageTitle}
+      ref={iframeRef}
+      src={iframeUrl}
+    />
+  );
+}
+
+Unit.propTypes = {
+  id: PropTypes.string.isRequired,
+  pageTitle: PropTypes.string.isRequired,
+};