Regex Tester & Validator

This regular expression matches relative URLs within a CSS `url()` function while deliberately ignoring absolute URLs that start with protocols like `http`, `https`, or `ftp`. It uses a negative lookahead to exclude these protocols and captures the path inside the `url()` function, handling optional surrounding quotes. This is particularly useful for build tools, asset bundlers, or scrapers that need to rewrite or localize relative asset paths in stylesheets.