Find browser’s default CSS rules

Authoritative references

Browsers ship default styles for many HTML elements like h1, input, p, and so on. You can find these default styles here:

• Chrome (Blink)
• Chrome/Safari (WebKit)
• Firefox (Gecko) Or, browse to resource://gre-resources/ and look at html.css.
• Internet Explorer (Trident) older versions

You can confirm that the above references show the correct default styles by using your browser’s DevTools. For example, in Chrome, default browser styles have the greyed out user agent stylesheet next to them:

Web UI to search styles

There’s also browserdefaultstyles.com that provides a web UI for searching those styles. This project seems to collect all the styles from the different browsers in one file and query that file from the web UI. I’m not sure how up to date its data is. Can look into it when I have more time.

Sources

• StackOverflow question