playground: fix web component constructor NotSupportedError

Author: jogibear9988

docs/playground.html

@@ -303,6 +303,10 @@ <h1>Playground</h1>
     super();
     const shadow = this.attachShadow({ mode: 'open' });
 
+    const style = document.createElement('style');
+    style.textContent = ':host{display:block;width:100%;height:100%}#editor{width:100%;height:100%}';
+    shadow.appendChild(style);
+
     // Add Monaco CSS inside the shadow root
     const link = document.createElement('link');
     link.rel = 'stylesheet';
@@ -311,9 +315,8 @@ <h1>Playground</h1>
 
     // Editor host div
     const div = document.createElement('div');
-    div.style.cssText = 'width:100%;height:100%';
+    div.id = 'editor';
     shadow.appendChild(div);
-    this.style.cssText = 'display:block;width:100%;height:100%';
 
     link.onload = () => {
       monaco.editor.create(div, {