0
0
SASSmarkup~7 mins

Critical CSS extraction strategies in SASS

Choose your learning style9 modes available
LearnWhyDeepRenderTryChallengeProjectRecallPerf
Introduction

Critical CSS helps your webpage load faster by showing important styles first. It makes the page look good quickly while other styles load in the background.

When you want your website's main content to appear quickly on screen.
If your page has many styles but only a few are needed right away.
To improve user experience on slow internet connections.
When optimizing for search engines that value fast loading pages.
If you want to reduce the chance of users leaving before the page loads.
Syntax
SASS
// Example of critical CSS in SASS
// Define critical styles separately
$critical-bg: #fff;
$critical-color: #333;

.critical {
  background-color: $critical-bg;
  color: $critical-color;
  font-weight: bold;
}

// Other styles load later
.other {
  color: #666;
  padding: 1rem;
}

Critical CSS is usually small and focused on above-the-fold content.

Use variables to keep critical styles consistent and easy to update.

Examples
This styles the main header quickly for fast display.
SASS
// Simple critical CSS block
.critical-header {
  font-size: 2rem;
  color: navy;
  margin: 0;
}
Adjusts critical styles for small screens to keep text readable.
SASS
// Critical CSS with media query
@media (max-width: 600px) {
  .critical-header {
    font-size: 1.5rem;
  }
}
Mixins help reuse critical style rules easily.
SASS
// Using SASS mixin for critical styles
@mixin critical-text {
  font-weight: 700;
  color: darkred;
}

.critical-alert {
  @include critical-text;
  background: #ffe0e0;
}
Sample Program

This example shows critical CSS in the <style> tag inside <head>. It styles the page background and header quickly. The rest of the styles come from an external file loaded later.

SASS
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <title>Critical CSS Example</title>
  <style>
    /* Critical CSS extracted and inlined */
    body {
      margin: 0;
      font-family: Arial, sans-serif;
      background-color: #fff;
      color: #222;
    }
    header {
      background-color: #007acc;
      color: white;
      padding: 1rem;
      font-size: 1.5rem;
      font-weight: bold;
    }
  </style>
  <link rel="stylesheet" href="styles.css" />
</head>
<body>
  <header>Welcome to My Site</header>
  <main>
    <p>This content loads styled after the critical CSS.</p>
  </main>
</body>
</html>
OutputSuccess
Important Notes

Keep critical CSS as small as possible to speed up loading.

Use tools or build steps to automatically extract critical CSS from your full styles.

Test on different devices to ensure critical styles cover all important content.

Summary

Critical CSS shows important styles first for faster page display.

Extract critical CSS by focusing on above-the-fold content and using SASS features like variables and mixins.

Inline critical CSS in the HTML head and load other styles separately for best performance.