JSFiddle - React, Tailwind, and code Playground

HTML

<button class="side-button">botão 1</button>
<button class="side-button">botão 2</button>
<div>Div 1</div>
<div>Div 2</div>

CSS

.side-button {
    color: blue;
}
.clicked-button {
    color: red;
}

JavaScript

var btns = document.querySelectorAll('button');
var show = document.querySelectorAll('div');

for (var i = 0; i < btns.length; i++) {
    (function () {
        var thisIndex = i;
        btns[i].addEventListener('click', function () {
            this.classList.remove('side-button');
            this.classList.add('clicked-button');
            show[thisIndex].style.display = 'initial';

            for (var j = 0; j < btns.length; j++) {
                if (j != thisIndex) {
                    btns[j].classList.remove('clicked-button');
                    btns[j].classList.add('side-button');
                    show[j].style.display = 'none';
                }
            }
        });
    })();
}