demo

code

<style>
.dropdown {
 position: relative;
 display: inline-block;
}
.dropdown-content {
 display: none;
 position: absolute;
 background-color: #f9f9f9;
 min-width: 160px;
 box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
 padding: 12px 16px;
 z-index: 1;
}
.dropdown:hover .dropdown-content {
 display: block;
}
</style>
<div class="dropdown">
 <span>Mouse over me</span>
 <div class="dropdown-content">
 <p>Hello World!</p>
 </div>
</div>