Explore the similarities and differences between pseudo-elements and pseudo-classes

Analysis of similarities and differences between pseudo-elements and pseudo-classes

Pseudo-element (pseudo-element) and pseudo-class (pseudo-class) are two important concepts in CSS , they play different roles in style selectors. This article will analyze the similarities and differences between pseudo-elements and pseudo-classes in detail, and illustrate them with specific code examples.

1. Pseudo-element

Pseudo-element creates a virtual sub-element inside the element, and you can apply styles to this virtual sub-element. Pseudo elements are represented by double colons "::", such as "::before" and "::after".

1.1 Create a virtual sub-element

In order to create a virtual sub-element, you can use the pseudo-element selector and specify the name of the pseudo-element. For example, the following code will insert a dummy element before the content of the element:

element::before {
   content: "Hello";
}

1.2 Set the style of the pseudo element

In the above code, we set the content attribute value to "Hello" to add text content to pseudo elements. In addition to the content attribute, you can also set other styles for pseudo elements, such as color, font-size, etc. The specific usage method is the same as setting the style of ordinary elements.

1.3 Usage scenarios of pseudo elements

Common usage scenarios of pseudo elements include:

1) Modify the content of the element, such as adding reference symbols, icons, etc.;
2) Insert some styles that match the element content, such as adding backgrounds, borders, etc.;
3) Create a block-level element to accommodate other elements.

2. Pseudo-class

Pseudo-class controls the style of elements in specific states. You can apply styles to specific states of elements through selectors. Pseudo-classes are represented by a single colon ":", such as ":hover" and ":nth-child(n)".

2.1 Commonly used pseudo-classes

There are many kinds of pseudo-classes. Commonly used pseudo-classes include:

1):hover: The style applied when the mouse hovers over the element. ;
2):active: The style applied when the element is clicked;
3):first-child: Select the first child element;
4):last-child: Select the last child element;
5):nth-child(n): Select the nth child element.

2.2 Usage scenarios of pseudo-classes

Pseudo-classes are often used for style control related to user interaction. For example, when the user hovers over a link, a specific style can be applied to the link; when the user clicks a button, a specific style can be applied to the button. In addition, pseudo-classes can also be used in conjunction with form elements to implement custom styles for form elements.

3. Similarities and differences between pseudo-elements and pseudo-classes

3.1 Similarities

• Pseudo-elements and pseudo-classes are both ways to select elements in CSS.
• Both pseudo-elements and pseudo-classes are represented by colons. Pseudo-elements use "::" and pseudo-classes use ":".
• Both pseudo-elements and pseudo-classes can apply specific styles to elements.

3.2 Differences

• Pseudo-element creates a virtual child element inside the element, while pseudo-class selects a specific state of the element.
• Pseudo elements are represented by double colon "::", and pseudo classes are represented by single colon ":".
• Pseudo elements can add new content to the element and apply styles to it, while pseudo classes can only apply styles to a specific state of the element. For example, a pseudo-element can insert a bracket at the beginning of a paragraph, while a pseudo-class can only apply styles when the mouse is hovering over a link.

Code example:

p::before {
   content: "(";
   color: red;
}

a:hover {
   color: blue;
}

In the above code, the pseudo element "::before" adds a bracket to the paragraph and sets its color to red. The pseudo-class ":hover" adds a mouse-over style to the link and sets the link's color to blue.

Summary:

This article provides a detailed analysis of pseudo-elements and pseudo-classes, and illustrates them through specific code examples. By understanding pseudo-elements and pseudo-classes, we can better use them to achieve various style effects and bring more possibilities to web design.

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