Hi @Palak@tru,

if I understand correctly you want sets your own styles for class.

These styles do not work?

 .classic-tabs .nav li a.active { 
    border-bottom: 5px solid blue !important; 
    transition: width 1s ease, 0.5s ease !important
 }

Please make you sure you correctly and in the right order you imported styles, like this:

import React from 'react';
import ReactDOM from 'react-dom';
import '@fortawesome/fontawesome-free/css/all.min.css';
import 'bootstrap-css-only/css/bootstrap.min.css';
import 'mdbreact/dist/css/mdb.css';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';

Please tell me if problem still exists.

Best regards, Konrad.