How to replace css images

In recent years, with the rapid development of Internet technology, more and more attention has been paid to the aesthetics of website pages. As an important design element in website design, pictures play an irreplaceable role. However, in the daily development process, appropriately changing the image can better adjust the web page style. CSS image replacement, as one of the important technical means, has gradually become known to web developers.

1. What is CSS image replacement?

Before introducing CSS image replacement, we need to understand some basic concepts about CSS calculated properties and display properties. Computed attributes can be simply understood as the final attribute values ​​generated by the browser parsing the style sheet and calculating it, including but not limited to text size, color, font style and other elements. The display attribute is the final rendered page style.

The principle of CSS image replacement is to replace the original image address in the attribute calculation stage to achieve the effect of changing the page image. Generally, we use the tag in HTML code to insert images, and then replace them through the CSS background attribute or content attribute.

2. Three ways to implement CSS image replacement

1. Use the background attribute to replace images

This is the most commonly used method. It is worth noting that in this method, you need to pay attention to the traffic problem of requesting images. Because the request method of the background image is a GET request (that is, requesting the server to download resources), and this request is performed together with HTML and JS code.

(1) Replace the image through the background attribute in the CSS file

Sample code:

.demo{
    width: 200px;
    height: 150px;
    background: url('./images/demo.png') no-repeat center center / contain;
}

In this example, we set the background image to demo.png, and It is set to be centered and adaptive to the width and height.
(2) Replace images through inline styles in HTML

Sample code:

<div style="width: 200px; height: 150px; background: url(&#39;./images/demo.png&#39;) no-repeat center center / contain;"></div>

2. Use the content attribute to replace images

The content attribute can Used to set pseudo elements, combined with pseudo classes such as :before or :after, to replace images through the content attribute. This method is widely used. It can not only replace pictures, but also produce more practical effects.

Sample code:

.demo:before{
    content: "";
    display: block;
    width: 200px;
    height: 150px;
    background: url('./images/demo.png') no-repeat center center / contain;
}

In this example, we use the :before pseudo-element to generate an alternative element with a width and height of 200px*150px, a background image of demo.png, and a centered display.

3. Use SVG sprite library to replace

SVG sprite library is a technical means similar to CSS sprite library. It first merges multiple SVG images, and selects the window position of a desired image through the CSS background-image and background-position properties to achieve the effect of image replacement.

Sample code:

.demo{
    width: 100px;
    height: 100px;
    background-image: url('./images/smile-icon.svg');
    background-position: -20px -10px;
}

In this example, we reference an SVG sprite library named smile-icon and take out the viewport position of the required picture through the background-position property .

3. Analysis of the advantages and disadvantages of CSS image replacement

For CSS image replacement technology, its advantages and disadvantages are obvious.

Advantages:

1. Strong flexibility

CSS image replacement technology can flexibly control the size and position of page images to meet the needs of different page design styles. need.

2. Reduce server requests

Through CSS image replacement, we can download the elements of the required image at one time through the CSS style sheet, thereby reducing server requests.

3. Improved page speed

The above method can reduce the number of requests and reduce page loading time, thereby improving page speed.

Disadvantages:

1. Impact on SEO

For search engines, when visitors search for content, they cannot obtain information about page images. Because search engines cannot read image information in CSS styles, this technology is not applicable to some websites that require SEO.

2. Not friendly to special users

For visitors who hope that visitors can disable CSS styles or use screen readers to read web pages, CSS image replacement will hinder their experience.

4. Summary

CSS image replacement technology is a very important part of web development. It can effectively optimize the display effect of page images. Through the methods introduced in this article, we can easily master the skills of CSS image replacement, thereby more easily achieving the page effects we want.

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