class TabComponent extends HTMLElement {
    constructor() {
        super();

        this.root = this.attachShadow({mode: "open"});

        this.root.innerHTML = `
            <style>
                /* CSS here */
            </style>
            
            <!-- HTML here -->    
        `;
    }

    connectedCallback() {
        /* Code here */
    }
}

window.customElements.define("tab-component", TabComponent);