New Twiddle

components.highlighter\.js

import Component from '@glimmer/component';
import { action } from '@ember/object';
import { task } from 'ember-concurrency'

export default class extends Component {
  
  @task * highlight() {
    document.querySelector(this.args.target)?.classList.add('highlight')
    yield new Promise((resolve) => setTimeout(resolve, 1))
    document.querySelector(this.args.target)?.classList.add('transition')
  }
  
  @action dismiss() {
    document.querySelector(this.args.target)?.classList.remove('highlight', 'transition')
  }
  
}

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;
}

.highlight {
  position: relative;
}

.highlight::before {
  /* Highlight color */
  background-color: #46b96c;
  content: "";
  position: absolute;
  width: 0%;
  opacity: 0%;
  height: 60%;
  left: -2px;
  bottom: 0;
  z-index: -1;
  transform: rotate(-1deg);
  transition: opacity 0.3s ease-in-out, width 0.3s ease-in-out;
}

/* #header {
    background: red;
    padding: 10px 0;
    position: relative;
    -webkit-transition: all 1s linear;
    -moz-transition: all 1s linear;
    -o-transition: all 1s linear;
    transition: all 1s linear;
    left:0;
} */

/* #header.transition {
    background: green;
    left: 50px;
} */

.highlight.transition::before {
  width: calc(100% + 4px);
  opacity: 100%;
}

.target {
  margin-top: 100px;
  font-size: 3rem;
}

templates.application\.hbs

<Highlighter @target='[data-test="target"]'>
	Term
</Highlighter>

<div class='target' data-test='target'>
	Target
 </div>

templates.components.highlighter\.hbs

<div ...attributes
	{{on 'mouseenter' (perform this.highlight)}}
  {{on 'mouseleave' this.dismiss}}
>
	{{yield}}
</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-concurrency": "2.2.1"
  }
}