JSFiddle - React, Tailwind, and code Playground

HTML

<h2 id="Panel" class=""><a href="#" >Title</a></h2>

<fieldset>
    <div class="FormItem">
        <p>Some text</p>
        <p>Some text</p>
        <p>Some text</p>
    </div>
    <div class="FormItem">
        <p>Some text</p>
        <textarea rows="2" cols="20" style="height: 40px;"></textarea>
    </div>
    <div class="FormItem">
        <p>Some text</p>
        <p>Some text</p>
        <p>Some text</p>
    </div>
</fieldset>

CSS

.alert-counter {
    color:red
}

JavaScript

jQuery(document).ready(function () {
    var textarea = $("h2#Panel").next("fieldset").find('.FormItem:nth-child(2) textarea');
    var counter = $("<div class='dnnLabel' style='position: relative;'><label><span id='counter'></span></label></div>");

    $(textarea).after(counter);
    $(textarea).CountCharacters({
        Start_Count: 0,
        Amount_Result: "counter",
        Alert_Class: "alert-counter",
        Amount_Limit: 19,
        maximumCharacters: 5
    });
});

(function ($) {

    $.fn.CountCharacters = function (options) {

        var defaults = {
            Start_Count: 0,
            Amount_Result: false,
            Alert_Class: false,
            maximumCharacters: 9
        }

        var options = $.extend(defaults, options);

        return this.each(function () {

            var characters = options.Start_Count;

            if (options.Amount_Result != false) {
                $("#" + options.Amount_Result).append("Aantal karakters: <strong>" + characters + "</strong>");
            }

            $(this).keyup(function () {
                if (options.Amount_Result != false) {
                    var number_of_characters = $(this).val().length;
                    $("#" + options.Amount_Result).html("Aantal karakters: <strong>" + number_of_characters + "</strong>");

                    if (number_of_characters >= options.maximumCharacters) {
                        $("#" + options.Amount_Result).addClass(options.Alert_Class);
                    } else {
                        $("#" + options.Amount_Result).removeClass(options.Alert_Class);
                    }
                }
            });

        });

    };

})(jQuery);