<script>
    class MyCustomElement extends HTMLElement {
        constructor() {
            super();
            this.addEventListener('click', () => alert('Custom Element Clicked'));
        }
        
        connectedCallback() {
            this.innerHTML = '<h1>Hello Custom Element</h1>';
        }
    }
    
    window.customElements.define('my-custom-element', MyCustomElement);
</script>
<my-custom-element></my-custom-element>

// Code goes here

/* Styles go here */