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Quick Tip #001—Inline Minified CSS

Originally posted on The Simplest Web Site That Could Possibly Work Well on zachleat.com

This tip works well on small sites that don’t have a lot of CSS. Inlining your CSS removes an external request from your critical path and speeds up page rendering times! If your CSS file is small enough, this is a simplification/end-around for Critical CSS approaches.

Installation Jump to heading

npm install clean-css to make the CSS minifier available in your project.

Configuration Jump to heading

Add the following cssmin filter to your Eleventy Config file:

const CleanCSS = require("clean-css");
module.exports = function(eleventyConfig) {
  eleventyConfig.addFilter("cssmin", function(code) {
    return new CleanCSS({}).minify(code).styles;
  });
};

Create your CSS File Jump to heading

Add a sample CSS file to your _includes directory. Let’s call it sample.css.

body {
    font-family: fantasy;
}

Capture and Minify Jump to heading

Capture the CSS into a variable and run it through the filter (this sample is using Nunjucks syntax)

<!-- capture the CSS content as a Nunjucks variable -->
{% set css %}
  {% include "sample.css" %}
{% endset %}
<!-- feed it through our cssmin filter to minify -->
<style>
  {{ css | cssmin | safe }}
</style>

Using JavaScript templates Jump to heading

Contributed by Zach Green

You can also inline minified CSS in a JavaScript template. This technique does not use filters, and instead uses async functions:

const fs = require("fs/promises");
const path = require("path");
const CleanCSS = require("clean-css");

module.exports = async () => `
<style>
  ${await fs
    .readFile(path.resolve(__dirname, "./sample.css"))
    .then((data) => new CleanCSS().minify(data).styles)}
</style>`;

Warning about Content Security Policy Jump to heading

If you are using a Content Security Policy on your website, make sure the style-src directive allows 'unsafe-inline'. Otherwise, your inline CSS will not load.