JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-2.2.1.min.js"></script>
<div class="b-form-wrap">
  <p id="validation-fail-msg">Please, fill in the missing fields.</p>
  <form novalidate id="feedback-form">
    <div class="b-form-box">
      <p class="form-box__text form-box__text_no-pad">What's your name?<sup class="form-box__sup">*</sup></p>
      <input type="text" name="name" maxlength="30" required id="name-input" class="form-box__input-field">
      <p class="form-box__text">What's your phone number?<sup class="form-box__sup">*</sup></p>
      <input type="text" name="phone" maxlength="30" required id="phone-input" class="form-box__input-field">
      <p class="form-box__text">What's your email?<sup class="form-box__sup">*</sup></p>
      <input type="text" name="email" maxlength="50" required id="email-input" class="form-box__input-field">
    </div>
    <div class="b-form-box b-form-box_left-mrg">
      <p class="form-box__text form-box__text_no-pad">How can I help you?</p>
      <textarea name="text" class="form-box__input-field form-box__input-field_textarea"></textarea>
    </div>
    <button class="form-box__button">Beautify me</button>
    <p id="validation-success-msg">Thanx, I'll contact you very soon.</p>
  </form>
</div>

JavaScript

$(document).ready(function(){
  $(".form-box__button").click(function(e){
    e.preventDefault();    
    if (feedback_validate()){
    	$.ajax({
     	 	type: "POST",
      	url: "php/feedback.php",
      	data: $(this).serialize()
   		}).done(function() {
      		$(this).find("input").val("");
      		$('#validation-success-msg').show('fast');
      		$("html, body").animate({
        		scrollTop: $(document).height()
      		}, "slow");
      $("#feedback-form").trigger("reset");
    });
    }
  });
});

function feedback_validate() {
  var result = true;
  var f_names = ["#name-input", "#email-input", "#phone-input"];
  var el;

  f_names.forEach(function(item) {
      el = $(item);
      if (el.val() == "") {
        result = false;
        el.addClass("validation-error");
      } else {
        el.removeClass("validation-error");
      }
  });

  if (result) {
    $("#validation-fail-msg").hide();
  } else {
    $("#validation-fail-msg").show();
    
    $('html, body').animate({
        scrollTop: $("#validation-fail-msg").offset().top
    }, 1000);

  }

	return result;
}