<button class="popup_open" id="popup_open">Button</button>
<div class="popup" id="popup">
<div class = "popup_body">
<div class="popup_content">
<button class="popup_close" id="popup_close">X</button>
<h1 class="popup_title">Подписаться</h1>
<div class="popup_forms">
<label class="name" for="name"><b>Name</b></label> <br>
<input type="text" placeholder="Your name" name="name" required> <br>
<label class="email" for="email"><b>E-mail</b></label> <br>
<input type="text" placeholder="Your e-mail" name="email" required><br>
</div>
</div>
</div>
</div>
.popup {
display: none;
let elem = document.getElementById('.popup')
document.getElementById('.popup_open').addEventListener ('click', () => elem.style.display = 'block'),
document.getElementById('.popup_close').addEventListener ('click', () => elem.style.display ='none');
