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CSS variables, or custom properties, are values defined with a -- prefix that can be reused throughout your CSS. They improve maintainability and allow dynamic styling.
CSS variables store reusable values like colors, fonts, or sizes. They are accessed using var().
:root defines global variables accessible anywhere in the document.var(--property-name) is used to retrieve the variable’s value.Example:
:root {
--primary-color: #3498db;
--secondary-color: #2ecc71;
--font-size: 16px;
}
body {
background-color: var(--primary-color);
color: var(--secondary-color);
font-size: var(--font-size);
}
<h1>Welcome to CSS Variables</h1>
<p>This paragraph uses global CSS variables for background, text color, and font size.</p>
Fallback values are used if a variable is not defined, ensuring consistent styling.
Example:
-text-color is not defined, the text will default to black.p {
color: var(--text-color, black); /* Fallback to black */
font-size: 18px;
padding: 15px 20px;
background-color: #e0e0e0;
border-radius: 8px;
text-align: center;
}
<p>This paragraph uses a CSS variable with a fallback color.</p>
Variables can be global (accessible everywhere) or local (restricted to a selector).
Example – Global:
Global variables are accessible anywhere.
:root {
--main-bg: #f0f0f0;
}
body {
background-color: var(--main-bg);
}
<h2>Global Variable Example</h2>
<p>The background color comes from a global CSS variable.</p>
Example – Local:
Local variables are only accessible within that selector and its children.
.card {
--card-bg: #fff;
background-color: var(--card-bg);
padding: 20px;
border-radius: 10px;
}
<div class="card">
<h2>Local Variable Example</h2>
<p>This paragraph uses a local variable for card background color.</p>
</div>
CSS variables can be updated dynamically with JavaScript for themes or interactive designs.
Example:
<button id="theme-btn">Switch Theme</button>
<p style="color: var(--primary-color)">This text color will change dynamically.</p>
<script>
const btn = document.getElementById("theme-btn");
btn.addEventListener("click", () => {
document.documentElement.style.setProperty('--primary-color', '#e74c3c');
});
</script>
Variables can be used in media queries to create responsive designs.
Example:
:root {
--font-size: 16px;
}
@media (max-width: 600px) {
:root {
--font-size: 14px;
}
}
body {
font-size: var(--font-size);
}
<p>Resize your browser to see the font size change using CSS variables in media queries.</p>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
:root {
--primary-color: #3498db;
--secondary-color: #2ecc71;
--font-size: 16px;
}
body {
background-color: var(--primary-color);
color: var(--secondary-color);
font-size: var(--font-size);
font-family: Arial, sans-serif;
text-align: center;
padding: 50px;
}
button {
padding: 10px 20px;
font-size: var(--font-size);
background-color: var(--secondary-color);
border: none;
cursor: pointer;
}
@media (max-width: 600px) {
:root {
--font-size: 14px;
}
}
</style>
</head>
<body>
<h1>CSS Variables Demo</h1>
<p>Resize the browser to see responsive changes in font size.</p>
<button>Click Me</button>
</body>
</html>