content屬性在CSS中用于向偽元素插入生成內(nèi)容。其核心作用是添加非HTML結(jié)構(gòu)中的視覺內(nèi)容，如文本、符號、圖片或自動計數(shù)器。1. 插入文本或符號：可用于添加標(biāo)簽或圖標(biāo)，如“Note: ”或Unicode字符；2. 添加圖像或計數(shù)器：支持插入圖片及實現(xiàn)自動編號；3. 樣式控制：可對生成內(nèi)容應(yīng)用樣式如字體、顏色和布局；4. 使用限制：應(yīng)避免用于關(guān)鍵信息或大量文本，以免影響可訪問性與維護性。

The content property in CSS is essential when working with pseudo-elements like ::before and ::after. Its main purpose is to insert generated content into the document tree—content that isn't present in the actual HTML markup but appears visually on the page.

Why Use content with Pseudo-Elements?

Pseudo-elements like ::before and ::after don’t do much on their own. If you try to style them without using the content property, they won’t show up at all. That’s because browsers ignore pseudo-elements unless there's something to display. The content property gives you a way to define what that "something" is.

Inserting Text or Symbols

One of the most common uses of content is inserting text or special characters before or after an element. This can be helpful for adding labels, icons, or decorative elements without modifying the HTML.

For example:

p::before {
  content: "Note: ";
  font-weight: bold;
}

This adds the word “Note: ” in bold at the beginning of every paragraph. You could use this to highlight warnings, tips, or other recurring messages.

You can also use Unicode characters or emojis:

li::before {
  content: "\2713"; /* Unicode checkmark */
  margin-right: 5px;
}

Just keep in mind:

• The inserted content is not selectable or searchable by users.
• It should not be used for important information that affects accessibility or SEO.

Adding Images or Counters

Besides text, you can use content to insert images or create automatic counters.

To insert an image:

div.banner::after {
  content: url("icon-star.png");
}

This places an image next to the banner without needing an <img alt="偽元素中內(nèi)容屬性的目的是什么？" > tag. It’s useful for small icons or decorative graphics.

For counters:

body {
  counter-reset: section;
}

h2::before {
  counter-increment: section;
  content: "Section " counter(section) ": ";
}

Now each heading will automatically be numbered as "Section 1", "Section 2", etc. This is great for documentation or long-form content where you want to organize sections dynamically.

Styling Generated Content

Once you've added content via content, you can style it just like any other element. You can apply margins, colors, fonts, and even positioning.

For example:

blockquote::before {
  content: open-quote;
  font-size: 2em;
  color: gray;
}

This adds a styled quotation mark before every blockquote. Common values include:

• open-quote / close-quote
• "string"
• url(image.jpg)
• counter(name)

You can also set properties like display, position, or float to control how the generated content behaves visually.

When Not to Use It

While content is powerful, it’s best used sparingly. Avoid inserting large chunks of text or anything that conveys critical meaning, since screen readers may not interpret it consistently. Also, overusing pseudo-elements can make styles harder to maintain.

In short, think of content as a tool for visual enhancements rather than structural content.

基本上就這些。

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