JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.2.1.js"></script>
<a class="topico1 topic exibir">1</a>
<a class="topico2 topic">2</a>
<a class="topico3 topic">3</a>
<a class="topico4-exibir topic">4</a>

CSS

.topic {
  color:#999;
}
.exibir {
  color: #000 !important;
}

JavaScript

$(document).on('click','.topic',function(){
	$('.topic').removeClass('exibir');
  $(this).addClass('exibir');
});