:hover usage in html and css - html

Question

Can anyone tell me where I can use :hover?
In the last CSS line it's .dropdown:hover .dropdown-content which gets me a dropdown menu when I hover on dropdown element.
However, if I use .dropbtn:hover .dropdown-content instead, no dropdown menu is displayed. Why is that?
ul {
list-style-type: none;
margin: 0;
padding: 0;
overflow: hidden;
background-color: #333;
}
li {
float: left;
}
li a {
display: inline-block;
color: white;
text-align: center;
padding: 14px 16px;
text-decoration: none;
}
li a:hover {
background-color: red;
}
.dropdown-content {
display: none;
position: absolute;
background-color: #f9f9f9;
min-width: 160px;
box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
z-index: 1;
}
.dropdown-content a {
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
text-align: left;
}
.dropdown-content a:hover {
background-color: #f1f1f1
}
.dropdown:hover .dropdown-content {
display: block;
}
<ul>
<li>Home</li>
<li>News</li>
<li class="dropdown">
Dropdown
<div class="dropdown-content">
Link 1
Link 2
Link 3
</div>
</li>
</ul>
<h3>Dropdown Menu inside a Navigation Bar</h3>
<p>Hover over the "Dropdown" link to see the dropdown menu.</p>

Answer 1

As per your code, The dropdown menu is a part of a list element.
<li class="dropdown">
Dropdown
<div class="dropdown-content">
Link 1
Link 2
Link 3
</div>
</li>
Your class "dropbtn" is a class which is applied for an anchor link you've placed. So that's why when you use the code
.dropbtn:hover .dropdown-content {
display: block;
}
It does not make sense, because the div with class "dropdown-content" is not a child of the element which contains the class "dropbtn" - which is a simple anchor element.
however, The code:
.dropdown:hover .dropdown-content {
display: block;
}
works becausue the class "dropdown" is the class of the parent element, which is the list element and then under it, we have the div with class "dropdown-content".
That's how CSS works and hope it makes sense.