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A set of reference stylesheets for EPUB Reading Systems.

Readium CSS provides styles for reflowable text:

• paged and scrolled views;
• a "patch" for HTML5 Suggested Rendering specific to publications (e.g. extra styles for hyphenation, breaks, etc.);
• default styles for unstyled ebooks;
• theming;
• user settings;
• a set of baselines and recommendations for accessibility, overrides, and internationalization.

BSD-3-Clause (http://opensource.org/licenses/BSD-3-Clause)

See license.txt.

The primary goal of Readium CSS is to provide Reading System implementers with reliable and modern styles for reflowable EPUB 2 and EPUB 3 files. In addition, it should provide good interoperability in the existing ecosystem, while not overriding authors’ styles unless strictly necessary.

Readium CSS stylesheets were not designed and should not be used for fixed-layout EPUB, nor other file formats like FB2, PRC, Mobi, TEI, etc.

Some issues, which may be raised during development, will be documented so that they can serve as a reference for revisions of the EPUB specification, and even future specifications.

Readium CSS is implemented in the Readium Mobile and Readium Web projects.

You will find it in:

• ts-toolkit
• swift-toolkit
• kotlin-toolkit

External use include:

• Thorium Desktop
• Thorium Web
• Zotero
• Vital Source

Active development is pulled in branch develop.

Building and testing are relying on npm packages and scripts. To initialize your clone/fork, first install dev dependencies:

npm install

In case you’re encountering an error with Puppeteer, make sure you’re using at least Node v.20.11.1 – it might work with an earlier version but only the latest LTS as of March 21, 2024 has been tested.

Then create reference bitmaps for visual regression testing:

npm run test:ref

To transpile all stylesheets using PostCSS:

npm run build

To test the updated styles and catch visual regression bugs:

npm run test

To update reference bitmaps after a bugfix:

npm run test:approve

Documentation can be accessed in docs.

You can alternatively download it as an EPUB file.