why we need root pseudo class if we can declare variables inside html
The :root pseudo-class and the html element can both be used to declare CSS variables, and in most cases, they serve the same purpose. However, there are a few reasons why you might choose to use :root over html for declaring variables:
1. Specificity
The :root pseudo-class has higher specificity than the html element. This can be beneficial in certain situations where you want to ensure that your CSS variables have a higher precedence over other styles.
- Example:
:root { --main-color: blue; } html { --main-color: red; } body { color: var(--main-color); /* Will be blue because :root has higher specificity */ }
2. Consistency and Clarity
Using :root is a convention in the CSS community for declaring CSS variables. This convention makes it clear to other developers that the CSS variables are intended to be global and accessible throughout the entire document.
- Example:
:root { --primary-color: #3498db; --secondary-color: #2ecc71; }
3. Future-Proofing
The :root pseudo-class specifically targets the root element of the document, which could theoretically be different from the html element in future specifications or different contexts (e.g., XML documents). Using :root makes your CSS more robust and adaptable to different environments.
Practical Example
Here’s a complete example demonstrating both methods:
Using :root
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Example with :root</title>
<style>
:root {
--primary-color: #3498db;
--secondary-color: #2ecc71;
--main-font: Arial, sans-serif;
}
body {
background-color: var(--primary-color);
font-family: var(--main-font);
color: white;
}
</style>
</head>
<body>
<h1>Hello, World!</h1>
<p>This example uses :root for CSS variables.</p>
</body>
</html>
Using html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Example with html</title>
<style>
html {
--primary-color: #3498db;
--secondary-color: #2ecc71;
--main-font: Arial, sans-serif;
}
body {
background-color: var(--primary-color);
font-family: var(--main-font);
color: white;
}
</style>
</head>
<body>
<h1>Hello, World!</h1>
<p>This example uses html for CSS variables.</p>
</body>
</html>