Explain the CSS `content` property used with pseudo-elements
Jul 16, 2025 am 01:02 AM
The content attribute of CSS is mainly used for pseudo-elements such as ::before and ::after, which are used to insert generated content. 1. Support strings, URLs, counters, attribute values and Unicode characters; 2. ::before insert content at the beginning of the element, ::after at the end; 3. The display effect can be controlled through styles, such as color, font, background, etc.; 4. Note that empty strings still occupy space, use of escape characters, cannot insert HTML elements, and browser compatibility issues.
The CSS content property is mainly used with pseudo-elements like ::before and ::after . It allows you to insert generated content into the document without needing to modify the HTML. This can be handy for adding small visual touches or decorative elements directly through CSS.
Here's how it works and what you need to know when using it.
What You Can Put in the content Property
You're not limited to just plain text. The content property accepts several types of values:
- Strings (eg,
"Read more"): Most common use, wraps in quotes. - URLs (eg,
url(image.png)): Useful for inserting images. - Counter values (eg,
counter(section)): For auto-numbering sections. - Attribute values (eg,
attr(data-tooltip)): Pulls value from an HTML attribute. - Unicode characters (eg,
\2713): Used for symbols or icons.
Example:
p::after {
content: " ?";
}This adds a pencil emoji after every paragraph — simple but effective for visual cues.
When to Use ::before vs ::after
Both pseudo-elements work similarly with content , but their placement differences:
-
::beforeinserts content at the beginning of the selected element. -
::afterinserts content at the end .
Use ::before if you want to prepare something, like an icon before a link:
a::before {
content: "? ";
} Use ::after when appending, such as adding “(external)” after external links:
a.external::after {
content: " (external)";
} Just remember, pseudo-elements won't show up unless you set the content property — that's a common gotcha.
Styling Generated Content
Generated content behaves like inline elements by default, but you can style it like any other element. Common styles include:
- Setting
displaytoblockorinline-blockfor layout control. - Applying colors, fonts, spacing, or even background images.
- Using positioning (
absolute,relative) for precision placement.
For example, making a styled tag badge:
.tag::after {
content: "New!";
background: red;
color: white;
padding: 2px 5px;
border-radius: 3px;
font-size: 0.8em;
margin-left: 5px;
}It looks small, but these details make a difference visually.
A Few Things to Watch Out For
- Empty strings still take space : If you do
content: "", it technically creates something — useful for clearfixes or invisible spaces. - Escaped characters matter : Want to insert a quote? Use
\"inside the string. - Not all HTML is allowed : You can't insert real HTML elements via
content, only plain text or images. - Older browsers may behave differently : Especially around quotes and escaping — test where needed.
Also, don't forget to check that your pseudo-element has a valid selector and that you're not missing a colon ( : ) or semicolon ( ; ). Typos happen.
Basically that's it. Once you get the hang of it, the content property becomes a go-to tool for clean, lightweight enhancements.
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