New Twiddle

components.panel-scroll-layout\.js

import Component from '@glimmer/component';

export default class extends Component {
}

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
}

templates.application\.hbs

<link href="https://unpkg.com/tailwindcss@^2/dist/tailwind.min.css" rel="stylesheet">

<PanelScrollLayout />

templates.components.app-footer\.hbs

<div class="p-3 bg-gray-800 text-gray-100 text-center">
  footer
</div>

templates.components.app-header\.hbs

<div class="p-3 bg-gray-800 text-gray-100 text-center">
  header
</div>

templates.components.panel-scroll-layout\.hbs

<div class="h-screen w-screen overflow-none flex flex-col">
  <div>
    <AppHeader />
  </div>
  
  <div class="flex-grow bg-gray-200">
    <div class="flex h-full">
      <div class="flex-grow bg-purple-100 text-center">
        Main content
      </div>
      
      <PortalTarget @name="summary-panel" />
    
      <Portal @target="summary-panel">
        <div class="bg-yellow-100 w-64">
          Summary panel
        </div>
      </Portal>
    </div>
  </div>
  
  <div>
    <AppFooter />
  </div>
</div>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0",
    "ember-stargate": "0.2.0"
  }
}