Master the skills and things to pay attention to when using common pseudo-classes and pseudo-elements in CSS

Learn the tips and precautions for using common pseudo-classes and pseudo-elements in CSS

CSS is an indispensable part of web development. It controls the layout of web pages. Style and layout. In CSS, pseudo-classes and pseudo-elements are powerful tools that can be used to select and modify specific parts of the page. This article will introduce the tips and precautions for using common pseudo-classes and pseudo-elements, and provide specific code examples.

1. Pseudo-class

1. :hover pseudo-class

:hover pseudo-class is used to change the style of an element when the mouse is hovering over it. Through the :hover pseudo-class, we can achieve hover effects, such as changing the color of links, the background color of buttons, etc.

Sample code:

a:hover {
color: red;
}

button:hover {
background-color: blue;
}

Note: It should be noted that the :hover pseudo-class can only be applied to interactive elements, such as links, buttons, etc.

2. :active pseudo-class

:active pseudo-class is used to change the style of an element when it is activated. Through the :active pseudo-class, we can achieve click effects, such as changing the background color when a button is pressed.

Sample code:

button:active {
background-color: green;
}

Note: It should be noted that: active pseudo-class Only takes effect when the element is clicked.

3. :nth-child pseudo-class

:nth-child pseudo-class is used to select a specific position of the element. We can select the nth child element through :nth-child(n), such as :nth-child(2) to select the second child element.

Sample code:

ul li:nth-child(even) {
background-color: lightgray;
}

Notes: Things to note Yes, n in the :nth-child pseudo-class starts counting from 1, not from 0.

2. Pseudo-element

1. ::before pseudo-element

::before pseudo-element is used to insert content before the content of the selected element. Through the ::before pseudo-element, we can insert icons, text, etc. in front of the element.

Sample code:

.box::before {
content: "prefix text";
}

Notes: It should be noted that, The ::before pseudo-element can only insert content in CSS and cannot be used in JavaScript or HTML.

2. ::after pseudo-element

::after pseudo-element is used to insert content after the content of the selected element. Through the ::after pseudo-element, we can insert icons, text, etc. behind the element.

Sample code:

.box::after {
content: "Post text";
}

Note: It should be noted that, The ::after pseudo-element can only insert content in CSS and cannot be used in JavaScript or HTML.

3. ::first-letter pseudo-element

::first-letter pseudo-element is used to select the first letter in the element and apply styles to it. Through the ::first-letter pseudo-element, we can achieve effects such as capitalizing the first letter and changing the style of the first letter.

Sample code:

p::first-letter {
font-size: larger;
color: red;
}

Notes : It should be noted that the ::first-letter pseudo-element can only select the first letter in the element.

3. Notes

1. Add two colons (::) before the selector of pseudo-classes and pseudo-elements to indicate that they are pseudo-elements, and only add one colon (:) to indicate that they are pseudo-elements. It's a pseudo class.
2. The names of pseudo-classes and pseudo-elements are case-sensitive and need to be written according to specifications.
3. When using pseudo classes and pseudo elements, they need to be used in conjunction with other selectors, such as element selectors, class selectors, etc.

Summary:

Pseudo classes and pseudo elements are powerful selectors in CSS and can achieve rich style effects. In the process of learning and using, we need to master the skills of using various pseudo-classes and pseudo-elements, and pay attention to following CSS specifications. By rationally using pseudo-classes and pseudo-elements, we can improve the interactivity and aesthetics of the page.

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