# What is CSS in EPUB?

Source: https://epublab.com/glossary/css-in-epub/ (updated 2026-11-03)

EPUB uses ordinary CSS stylesheets for presentation, but reading apps may override fonts, margins and colours, and some properties, such as fixed positioning, are unreliable or not allowed. Good EPUB CSS is short and lets the reader decide.

## Why it matters when you convert a PDF to EPUB

A PDF has exact fonts, sizes and positions for every line; copying them into CSS produces an EPUB that fights the reader's settings. A converter should keep only structure-related style (headings, emphasis, block quotes, note sizes) and drop absolute sizes and positions.