JSFiddle - React, Tailwind, and code Playground

HTML

<div class="item1"></div>
<div class="item2"></div>

CSS

.item1 {
  position: relative;
  width: 100px;
  padding: 100px;
  background-color: red;
}
.item2 {
  position: relative;
  width: 100px;
  padding: 100px;
  background-color: green;
}

JavaScript

$(document).on('mouseenter', '.item1', function(){
	$(this).append('<div class="dates-btn"><button type="submit">Добавить</button></div>');
});
$(document).on('mouseleave', '.item1', function(){
	$('.dates-btn').remove();
});