css_inline is a high-performance library for inlining CSS into HTML 'style' attributes.
This library is designed for scenarios such as preparing HTML emails or embedding HTML into third-party web pages.
For instance, the crate transforms HTML like this:
<html>
<head>
<style>h1 { color:blue; }</style>
</head>
<body>
<h1>Big Text</h1>
</body>
</html>into:
<html>
<head></head>
<body>
<h1 style="color:blue;">Big Text</h1>
</body>
</html>- Uses reliable components from Mozilla's Servo project
- Inlines CSS from
styleandlinktags - Removes
styleandlinktags - Resolves external stylesheets (including local files)
- Optionally caches external stylesheets
- Works on Linux, Windows, and macOS
- Supports HTML5 & CSS3
- Bindings for Python, Ruby, JavaScript, Java, C, and a WebAssembly module to run in browsers.
- Command Line Interface
If you'd like to try css-inline, you can check the WebAssembly-powered playground to see the results instantly.
To include it in your project, add the following line to the dependencies section in your project's Cargo.toml file:
[dependencies]
css-inline = "0.17"The Minimum Supported Rust Version is 1.75.
const HTML: &str = r#"<html>
<head>
<style>h1 { color:blue; }</style>
</head>
<body>
<h1>Big Text</h1>
</body>
</html>"#;
fn main() -> css_inline::Result<()> {
let inlined = css_inline::inline(HTML)?;
// Do something with inlined HTML, e.g. send an email
Ok(())
}Note that css-inline automatically adds missing html and body tags, so the output is a valid HTML document.
Alternatively, you can inline CSS into an HTML fragment, preserving the original structure:
const FRAGMENT: &str = r#"<main>
<h1>Hello</h1>
<section>
<p>who am i</p>
</section>
</main>"#;
const CSS: &str = r#"
p {
color: red;
}
h1 {
color: blue;
}
"#;
fn main() -> css_inline::Result<()> {
let inlined = css_inline::inline_fragment(FRAGMENT, CSS)?;
Ok(())
}css-inline can be configured by using CSSInliner::options() that implements the Builder pattern:
const HTML: &str = "...";
fn main() -> css_inline::Result<()> {
let inliner = css_inline::CSSInliner::options()
.load_remote_stylesheets(false)
.build();
let inlined = inliner.inline(HTML)?;
// Do something with inlined HTML, e.g. send an email
Ok(())
}inline_style_tags. Specifies whether to inline CSS from "style" tags. Default:truekeep_style_tags. Specifies whether to keep "style" tags after inlining. Default:falsekeep_link_tags. Specifies whether to keep "link" tags after inlining. Default:falsekeep_at_rules. Specifies whether to keep "at-rules" (starting with@) after inlining. Default:falseminify_css. Specifies whether to remove trailing semicolons and spaces between properties and values. Default:falsebase_url. The base URL used to resolve relative URLs. If you'd like to load stylesheets from your filesystem, use thefile://scheme. Default:Noneload_remote_stylesheets. Specifies whether remote stylesheets should be loaded. Default:truecache. Specifies cache for external stylesheets. Default:Noneextra_css. Extra CSS to be inlined. Default:Nonepreallocate_node_capacity. Advanced. Preallocates capacity for HTML nodes during parsing. This can improve performance when you have an estimate of the number of nodes in your HTML document. Default:32
You can also skip CSS inlining for an HTML tag by adding the data-css-inline="ignore" attribute to it:
<head>
<style>h1 { color:blue; }</style>
</head>
<body>
<!-- The tag below won't receive additional styles -->
<h1 data-css-inline="ignore">Big Text</h1>
</body>The data-css-inline="ignore" attribute also allows you to skip link and style tags:
<head>
<!-- Styles below are ignored -->
<style data-css-inline="ignore">h1 { color:blue; }</style>
</head>
<body>
<h1>Big Text</h1>
</body>Alternatively, you may keep style from being removed by using the data-css-inline="keep" attribute.
This is useful if you want to keep @media queries for responsive emails in separate style tags.
Such tags will be kept in the resulting HTML even if the keep_style_tags option is set to false.
<head>
<!-- Styles below are not removed -->
<style data-css-inline="keep">h1 { color:blue; }</style>
</head>
<body>
<h1>Big Text</h1>
</body>Another possibility is to set keep_at_rules option to true. At-rules cannot be inlined into HTML therefore they
get removed by default. This is useful if you want to keep at-rules, e.g. @media queries for responsive emails in
separate style tags but inline any styles which can be inlined.
Such tags will be kept in the resulting HTML even if the keep_style_tags option is explicitly set to false.
<head>
<!-- With keep_at_rules=true "color:blue" will get inlined into <h1> but @media will be kept in <style> -->
<style>h1 { color: blue; } @media (max-width: 600px) { h1 { font-size: 18px; } }</style>
</head>
<body>
<h1>Big Text</h1>
</body>If you set the the minify_css option to true, the inlined styles will be minified by removing trailing semicolons
and spaces between properties and values.
<head>
<!-- With minify_css=true, the <h1> will have `style="color:blue;font-weight:bold"` -->
<style>h1 { color: blue; font-weight: bold; }</style>
</head>
<body>
<h1>Big Text</h1>
</body>If you'd like to load stylesheets from your filesystem, use the file:// scheme:
const HTML: &str = "...";
fn main() -> css_inline::Result<()> {
let base_url = css_inline::Url::parse("file://styles/email/").expect("Invalid URL");
let inliner = css_inline::CSSInliner::options()
.base_url(Some(base_url))
.build();
let inlined = inliner.inline(HTML);
// Do something with inlined HTML, e.g. send an email
Ok(())
}For resolving remote stylesheets it is possible to implement a custom resolver:
#[derive(Debug, Default)]
pub struct CustomStylesheetResolver;
impl css_inline::StylesheetResolver for CustomStylesheetResolver {
fn retrieve(&self, location: &str) -> css_inline::Result<String> {
Err(self.unsupported("External stylesheets are not supported"))
}
}
fn main() -> css_inline::Result<()> {
let inliner = css_inline::CSSInliner::options()
.resolver(std::sync::Arc::new(CustomStylesheetResolver))
.build();
Ok(())
}You can also cache external stylesheets to avoid excessive network requests:
use std::num::NonZeroUsize;
#[cfg(feature = "stylesheet-cache")]
fn main() -> css_inline::Result<()> {
let inliner = css_inline::CSSInliner::options()
.cache(
// This is an LRU cache
css_inline::StylesheetCache::new(
NonZeroUsize::new(5).expect("Invalid cache size")
)
)
.build();
Ok(())
}
// This block is here for testing purposes
#[cfg(not(feature = "stylesheet-cache"))]
fn main() -> css_inline::Result<()> {
Ok(())
}Caching is disabled by default.
css-inline typically inlines HTML emails within hundreds of microseconds, though results may vary with input complexity.
Benchmarks for css-inline==0.17.0:
- Basic: 4.10 µs, 230 bytes
- Realistic-1: 84.30 µs, 8.58 KB
- Realistic-2: 57.31 µs, 4.3 KB
- GitHub page: 135.06 ms, 1.81 MB
These benchmarks, conducted using rustc 1.87 on Ryzen 9 9950X, can be found in css-inline/benches/inliner.rs.
Install with cargo:
cargo install css-inline
The following command inlines CSS in multiple documents in parallel. The resulting files will be saved
as inlined.email1.html and inlined.email2.html:
css-inline email1.html email2.html
For full details of the options available, you can use the --help flag:
css-inline --help
If you're interested in learning how this library was created and how it works internally, check out these articles:
If you have any questions or discussions related to this library, please join our gitter!
This project is licensed under the terms of the MIT license.
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