fix(custom-element): prevent injecting child styles if shadowRoot is false

Author: edison1105

packages/runtime-dom/src/apiCustomElement.ts

@@ -661,7 +661,9 @@ export class VueElement
    * @internal
    */
   _injectChildStyle(comp: ConcreteComponent & CustomElementOptions): void {
-    this._applyStyles(comp.styles, comp)
+    if (this._def.shadowRoot !== false) {
+      this._applyStyles(comp.styles, comp)
+    }
   }
 
   /**