Advanced CSS selector properties: pseudo-classes and pseudo-elements

Advanced CSS selector attributes: pseudo-classes and pseudo-elements

Introduction:
In CSS, selectors are an important concept that can help Developers accurately select DOM elements and apply styles. In addition to common element selectors (such as tag selectors and class selectors), CSS also provides two selector attributes, pseudo-class and pseudo-element, which can further enhance the functionality of selectors. This article will introduce the usage of pseudo-classes and pseudo-elements, and provide specific code examples, hoping to help readers better understand and apply these two properties.

1. Pseudo-classes:
Pseudo-class is a CSS selector that can select elements under specific states or conditions. Common pseudo-classes include :hover (mouse hover), :visited (link has been visited), :focus (get focus), etc. Here are some usage examples of pseudo-classes:

1. Mouseover style:
   :hover is used to select the style on which the mouse is hovering over the element. For example, we can set a mouseover style for the button:

button:hover { background-color: red; }

2. Visited link style:
   :visited The style used to select the visited link. For example, we can underline the visited link:

a:visited { text-decoration: underline; }

3. Get focus style:
   :focus The style used to select the element that is currently focused. For example, we can add a style to the input box when it gets focus:

input:focus { outline: 2px solid blue; }

2. Pseudo-elements:
Pseudo-elements are another selector of CSS. Specific parts of DOM elements can be selected. Common pseudo-elements include ::before (insert content before the element), ::after (insert content after the element), etc. Here are some examples of pseudo-element usage:

1. Insert content:
   ::before and ::after are used to insert specified content before or after the content of the element. For example, we can add brackets before and after a paragraph:

p::before { content: "("; } p::after { content: ")"; }

2. Clear floats:
   ::after is also commonly used to clear floats. When the parent element contains a floated element, you can use ::after to add an empty content to it and clear the float by setting the clear attribute:

.clearfix::after { content: ""; display: table; clear: both; }

3. Modify the first letter style:
   ::first-letter is used to select the first letter in the element and apply styles. For example, we can set the first letter to uppercase:

p::first-letter { text-transform: uppercase; }

Conclusion:
Pseudo classes and pseudo elements are important attributes in CSS to further enhance the functionality of selectors, and they can help development or accurately select DOM elements and apply styles. In actual development, we can choose to use pseudo-classes and pseudo-elements according to specific needs to achieve richer style effects. Through the introduction and sample code of this article, I believe that readers have a preliminary understanding of pseudo-classes and pseudo-elements, and I hope it can help readers better master and apply these two attributes.

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