Detailed explanation of the usage of CSS pseudo-classes and pseudo-elements and the differences between them

Detailed explanation of the difference and usage of CSS pseudo-classes and pseudo-elements

Pseudo-classes and pseudo-elements are concepts often used in CSS. They can help us select and style ize specific elements in HTML. Although their names are similar, they have different usage and functions. In this article, we will explain the difference between CSS pseudo-classes and pseudo-elements in detail and give specific code examples.

1. Pseudo-classes
First, let’s explain pseudo-classes. Pseudo-classes are selectors used to select and style specific states or properties in the DOM tree (Document Object Model). Pseudo-classes are usually represented by a colon (:).

1. :hover pseudo-class
   : The hover pseudo-class is used to apply styles when the mouse is hovering over an element. It can be applied to any HTML element.

For example, when the mouse hovers over a link, we can change the color of the link through the :hover pseudo-class:

a:hover {
  color: red;
}

2. :active pseudo-class
   The :active pseudo-class is used to apply styles when the user activates the element, such as a mouse click on a link.

For example, we can change the background color of the button when the user clicks the button:

button:active {
  background-color: yellow;
}

3. :nth-child pseudo-class
   :nth-child pseudo-class is used To select a child element at a specific position under the same parent element.

For example, we can select the even rows in the table and style them:

tr:nth-child(even) {
  background-color: #f2f2f2;
}

2. Pseudo-elements
Next, let’s do Let’s talk about pseudo-elements. Pseudo-elements are used to create and style new elements in the DOM. Pseudo elements are usually represented by double colons (::).

1. ::before pseudo-element
   ::before pseudo-element is used to create and insert content in front of the selected element. It can be used to add some decorative elements such as icons or other additional textual content.

For example, we can add a comment in front of the paragraph:

p::before {
  content: "注：";
  font-weight: bold;
}

2. ::after pseudo-element
   ::after pseudo-element is used to add a comment to the selected element. Create and insert content at the end of . It can also be used to add some decorative elements or additional textual content.

For example, we can add an arrow icon at the end of the link:

a::after {
  content: " →";
}

3. ::first-letter pseudo-element
   ::first-letter pseudo-element with Used to select the first letter of an element and style it. It can only be applied to block-level elements.

For example, we can set the first letter of the paragraph to uppercase and change its color:

p::first-letter {
  font-size: 2em;
  text-transform: uppercase;
  color: blue;
}

Summary:
To summarize, pseudo-classes and pseudo-elements in CSS are very useful tools that help us select and style different states and specific parts of HTML elements. Pseudo-classes are mainly used to select elements in a specific state, while pseudo-elements are mainly used to create and style new elements. Through the flexible use of pseudo-classes and pseudo-elements, we can better control and design our web pages.

I hope this article will help you understand and use CSS pseudo-classes and pseudo-elements!

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