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: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'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.