title: I have imported app component in app.module.ts file but still is not working
body: <p><code>'app-header'</code> is not a known element:</p>
  
  <ol>
  <li>If <code>'app-header'</code> is an Angular component, then verify that it is part of this module.</li>
  <li>If <code>'app-header'</code> is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message. ("wrapper">   
    [ERROR ->]   </li>
  </ol>