Application and implementation effect of CSS::before pseudo-element selector

Application and implementation effect of CSS::before pseudo-element selector

CSS::before pseudo-element selector is a commonly used pseudo-class selector in CSS , which can insert a virtual element in front of the element's content and can be decorated and beautified through CSS styles. In this article, we will introduce the application and implementation effects of the ::before pseudo-element selector, and provide specific code examples for reference.

1. Application scenarios

1. Text decoration: insert icons, labels, images and other content in front of the text to enhance the expressiveness of the text;
2. Picture decoration: in Add shadows, borders or other effects in front of the picture to enhance the beauty of the picture;
3. List decoration: add a logo or serial number to the list item to increase the readability of the list;
4. Custom label: pass ::before pseudo-element selector to achieve customized label effects;
5. Background decoration: Use the ::before pseudo-element selector to add background, border and other effects to container elements.

2. Implementation effect example

1. Text decoration example

<style>
  .icon::before {
    content: "002";
    font-family: "Font Awesome 5 Free";
    color: red;
    margin-right: 5px;
  }
</style>

<p class="icon">CSS ::before伪元素选择器示例</p>

Through the above code, we use the Font Awesome icon library to decorate the text Added an icon and set the red color and right margin.

2. Picture decoration example

<style>
  .image-container::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    opacity: 0;
    transition: opacity 0.3s ease;
  }
  
  .image-container:hover::before {
    opacity: 1;
  }
</style>

<div class="image-container">
  <img src="example.jpg" alt="Example Image">
</div>

In the above code, we add a translucent black mask to the picture container. When the mouse hovers over the picture, The transparency of the mask becomes 1, realizing the beautification effect of the picture.

3. List decoration example

<style>
  ul li::before {

    color: red;
    margin-right: 5px;
  }
</style>

<ul>
  <li>列表项一</li>
  <li>列表项二</li>
  <li>列表项三</li>
</ul>

In the above code, we use solid dots as the symbol of the list to achieve the decorative effect of the list items.

4. Custom tag example

<style>
  .custom-tag::before {
    content: "Tag: ";
    font-weight: bold;
  }
</style>

<p class="custom-tag">自定义标签示例</p>

In the above code, we add a custom tag to the paragraph, which is implemented through the ::before pseudo-element selector.

5. Background decoration example

<style>
  .container::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-image: url(background.jpg);
    background-size: cover;
    opacity: 0.5;
    z-index: -1;
  }
  
  .content {
    position: relative;
    z-index: 1;
  }
</style>

<div class="container">
  <div class="content">
    <h1>背景装饰示例</h1>
    <p>这是一段示例文本。</p>
  </div>
</div>

In the above code, we added a background image to the container element and set the opacity to 0.5 through the z-index attribute to control its level and achieve the decorative effect of the background.

3. Summary

Through the CSS ::before pseudo-element selector, we can achieve a variety of decorative effects and add more beauty and expressiveness to web page elements. When using the ::before pseudo-element selector, we need to pay attention to the way the selector is written, specify the inserted content through the content attribute, and decorate and beautify it through other CSS styles. I hope the sample code provided in this article can help you better understand and apply the ::before pseudo-element selector.

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