ReliCSS Digs Up the CSS Fossils Hiding in Your Stylesheets
Every codebase has a few skeletons in its CSS closet—a legacy !important that could be reined in with cascade layers, a checkbox hack that :has() now makes obsolete, or a pile of vendor-prefixed properties from a 2012-era redesign. Stu Robson’s ReliCSS tool is built to excavate outdated CSS and point out where modern solutions can take over.
Each relic gets a severity rating to help prioritize cleanup:
- High Severity: True “fossils”. Hacks for (now) unsupported browsers (IE6/7) or “dangerous” techniques. High-risk, obsolete, should be first targets for removal.
- Medium Severity: The middle ground. Hacks for older unsupported browsers (IE8-10). They work but they’re fragile. Hacks to review to see if they’re still relevant for your actual users.
- Low Severity: Modern artifacts. Usually vendor prefixes (-webkit-, -moz-). Safe mostly, but better handled by automated tools like Autoprefixer. They’re an opportunity to improve your build process.
Of course, no one is immune. Personal sites go years without overhauls, and there are always things in there that are embarrassing to admit. Even CSS-Tricks itself went at least five years between redesigns—and running ReliCSS against it turned up mostly vendor prefixing, likely from an older Autoprefixer configuration.
