CSS Performance - Optimization Techniques

What is CSS Performance?

CSS performance refers to how efficiently your styles are loaded, parsed, and rendered by the browser.

Performance Tips

1. Minimize CSS File Size

Minify CSS:

/* Before minification */
.button {
    background-color: #007bff;
    padding: 10px 20px;
}

/* After minification */
.button{background-color:#007bff;padding:10px 20px}

2. Reduce Selector Complexity

Slow:

div#header nav ul li a.active { }

Fast:

.nav-link-active { }

3. Use Transform and Opacity for Animations

Slow (triggers layout):

.box {
    transition: width 0.3s, height 0.3s;
}

Fast (GPU-accelerated):

.box {
    transition: transform 0.3s, opacity 0.3s;
}

4. Avoid @import

Slow:

@import url('styles.css');

Fast:

<link rel="stylesheet" href="styles.css">

5. Critical CSS

Load critical CSS inline, defer non-critical:

<style>
    /* Critical above-the-fold CSS */
    .header { }
</style>

<link rel="preload" href="styles.css" as="style" onload="this.onload=null;this.rel='stylesheet'">

6. Use will-change Sparingly

.animated-element {
    will-change: transform; /* Hint to browser */
}

/* Remove after animation */
.animated-element.done {
    will-change: auto;
}

CSS Performance - Optimization Techniques

On this page