how to add dropdown button in html

<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> 

<div class="dropdown">
  <button class="dropbtn">Dropdown</button>
  
<div class="dropdown-content">
    <a href="#">Link 
1</a>
    
<a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
</div>