JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" id="btnClick" value="Submit" /><br><textarea id="txt"></textarea>

CSS

.c1 {
    height:40px;
}
.c2 {
    height:250px;
}

JavaScript

$(document).ready(function () {
    var field = $("#txt");
    var btn = $("#btnClick");
    field.on("focusin", f1);
    field.on("focusout", f2);
    btn.on("click", f3);

    function f1() {
        field.removeClass("c1").addClass("c2");
    }

    function f2() {
        field.removeClass("c2").addClass("c1");
    }

    function f3() {
        alert('hi');
    }

});