JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="txtarea">texto a copiar</textarea>
<button id="copyBtn">Copiar</button>
<span id="copyMsg">Apreta Ctrl+C para copiar (Cmd + C en Mac)</span>

CSS

#copyMsg {
    visibility:hidden;
}

JavaScript

var txtarea = document.getElementById('txtarea');
    var copyBtn = document.getElementById('copyBtn');
    var copyMsg = document.getElementById('copyMsg');

    copyBtn.onclick = function () {
        txtarea.focus();
        txtarea.select();
        copyMsg.style.visibility = "visible";
    };