css replacement image

In web page production, pictures are a very important part, and when using CSS for web page style design, it often involves the replacement of some pictures. This article will introduce the methods and techniques of replacing images in CSS.

1. Background-image attribute

In CSS, you can use the background-image attribute to specify a background image. The specific method is to use the following statement in the CSS rule:

background-image: url("images/bg.jpg");

The image address within the quotes in url() is the image path to be replaced. It should be noted that the path here is relative to the HTML file itself. If a relative path is used to introduce a CSS file in HTML, the image path in the CSS file should also be based on the path relative to the HTML file.

2. Pseudo elements: before and :after

In CSS, pseudo elements refer to creating a virtual element that does not exist in the document tree through CSS styles. When using pseudo elements, you can operate them like ordinary elements, such as setting their size, background and other attributes.

When replacing a picture, you can use pseudo elements to add an additional element to achieve the effect of adding a picture. The specific method is as follows:

.selector:before {
    content: url("images/xxx.png");
}

In the above statement, .selector indicates the element selector to replace the image, and :before indicates the use of the pseudo element: before. In the content attribute, you can specify the image path to be replaced.

It should be noted that when using :before or :after, you need to set the content attribute for it, otherwise the element will not be rendered.

3. data-URI

In addition to using external image files for replacement, CSS also provides the data-URI method to directly embed images into CSS files in the form of Base64 encoding. This achieves an effect similar to pseudo-elements.

The specific method is to convert the image into Base64 encoding and reference it as a parameter of url() in the CSS style. For example:

background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAboAAAAeCAYAAABx68HMAAAACXBIWXMAAC4jAAAuIwF4pT92AAAAB3RJTUUH4goJ
CwohK6HlJQAAAN9JREFUKM+1kktugjAQxV/YRlLCTURzR91i9CGdqutj6zzDJj0moR9k6dpig7Oy4Bw+W0VNF/czNMcxqiX/wV9FzPE2DzjHyy/jVpefCvzXdCBN9+7Z
TDDNwqsOo +x +8/gqgGJr2HmJ4+kX9C0pvgCv3teUPpEWoFJpALyxqsdmFedW2++krT / JWbXEWddLqEBWLt + 8DfMvqNFL/QFSjufVYrk5Dr/tFNSSUZLTELPVdQAAAABJRU5ErkJggg==);

The advantage of this method is that it can reduce HTTP requests, thereby improving the loading speed of web pages. However, it should be noted that Base64 encoding will cause the image content to become larger, which will cause the page loading speed to decrease when using large images, so a trade-off needs to be made based on the specific situation.

In short, replacing images is a common style design requirement in web page production, and CSS provides a variety of ways to achieve this requirement. It is necessary to choose the appropriate method according to the actual situation, so as to make the page effect more excellent.

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