Slidein

components.my-component\.js

import Component from '@ember/component';

export default Component.extend({
  actions: {
    toggle(){
      this.set("shouldShow", !this.shouldShow);
    }
  }
})

controllers.application\.js

import Controller from '@ember/controller';

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

styles.app\.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}
.update-banner {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  width: 100%;
  background-color: yellow;

  overflow: none;
  animation: slidein 1s linear;
  animation-fill-mode: forwards;
}

@keyframes slidein {
  from {
    height: 0px;
  }

  to {
    height: 50px;
  }
}

templates.application\.hbs

<br>
<br>
{{outlet}}
<br>
<br>
{{my-component}}

templates.components.my-component\.hbs

{{#if shouldShow}}
  <div class="update-banner"></div>  
{{/if}}
<button {{action "toggle"}}>Click me</button>

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"
  }
}