JSFiddle - React, Tailwind, and code Playground

HTML

<form role='form' id='formCad' name='formCad' method='post'>
  <p><input type='text' id='input1' name='input1'></p>
  <br>
  <p><input type='text' id='input2' name='input2'></p>
  <br>
  <button id='btnCad' class='btn btn-default'>Cadastrar</button>
</form>

<div style="display:none;" class="alert alert-warning floating_alert alert1"><button type="button" class="close" data-dismiss="alert">x</button><strong style="color: red;">Atenção!</strong> Preencha o campo input1</div>

<div style="display:none;" class="alert alert-warning floating_alert alert2"><button type="button" class="close" data-dismiss="alert">x</button><strong style="color: red;">Atenção!</strong> Preencha o campo input2</div>

CSS

.floating_alert {
		position: fixed; 
		top: 0px; 
		left: 0px; 
		width: 100%;
		z-index: 9999;
		border-radius: 0px;
		font-size: 18px;
	}
	.alert {
		padding: 18px 35px 18px 14px;
		margin-bottom: 14px;
		color: #FFFFFF;
		background-color: #0158AA;
		border: 1px solid #FFFFFF !important;
		-webkit-border-radius: 0px;
		-moz-border-radius: 0px;
		border-radius: 0px;
	}
	.alert .close {
		position: relative;
		top: -2px;
		right: -21px;
		line-height: 18px;
	}
	.close {
		float: right;
		font-size: 21px;
		font-weight: 700;
		line-height: 1;
		color: #FFFFFF;
		text-shadow: none;
		filter: alpha(opacity=20);
		opacity: .2;
	}
	.alert-success,
	.alert-danger {
		color: #FFFFFF;
		background-color: #0158AA;
		border-color: #FFFFFF;
	}

JavaScript

$(document).ready(function(){
 
  $("button#btnCad").on('click', function(){

    var input1 = $("#input1").val();
    var input2 = $("#input2").val();

    if(input1 == "") {
      $(".alert1").fadeTo(3000,500).slideUp(500,function(){
        $(".alert1").slideUp(500);
        $(".alert1").remove();
      });
      $( "#input1" ).focus();
      return false;
    }

    if(input2 == "") {
      $(".alert2").fadeTo(3000,500).slideUp(500,function(){
        $(".alert2").slideUp(500);
        $(".alert2").remove();
      });
      $( "#input2" ).focus();
      return false;
    }

  });

});