JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" class="digs" maxlength="5"><strong class="err" style="display: none;"></strong>

CSS

strong {
    display: none;
    background-color: #E1E4F2;
    color: #F00;
    border: 1px solid #000;
    border-radius: 5px;
    position: absolute;
    left: 40%;
    padding: 5px;
    box-shadow: 0px 0px 10px #6E6E80;
    z-index: 1;
}

JavaScript

$(document).ready(function(){
     $('input[class=digs]').keypress(function(e){
     if(e.which != 8 && e.which != 0 && (e.which < 48 || e.which > 57)){
     $(this).next().html("Sadece rakam").show().fadeOut(3000);
     return false;
     }
     });
     //$('input[class=digs]:first').focus();
     });