JSFiddle - React, Tailwind, and code Playground

HTML

<a href='#' class='vhod'>Вход</a>

<div class='fon'></div>
    
<form action='' method='post' class='vvod'>
    Логин<br>
    <input type='text' name='log'><br>
    Пароль<br>
    <input type='text' name='pass'><br>
    <br>
    <input type='text' name='' value='Врйти'><br>
 </form>

CSS

.vvod {
  display: none;
  top:50px;
  left:100px;
  position: absolute;
}

.fon {
    display: none;
    position: absolute;
    width: 100%; height: 100%;
    top:0px;
    background-color: #000;
    opacity: 0.5;
    }

JavaScript

$(document).ready(function(){
    
    $(document).on('click', function (e) {
        if ($('form').has(e.target).length === 0){
                $('.fon').fadeOut();
                $('.vvod').fadeOut();
        }})
        
        $('.vhod').click(function(){
            $('.fon').fadeIn();
            $('.vvod').fadeIn();
        });
    
});