Where is the default stylesheet for Chrome extension popups and options pages?

Question

Popups and Options Pages for Chrome extensions have an additional user agent stylesheet that adds styles similar to Chrome's own chrome://settings and other pages. The styles are mentioned in explaining how to declare your V2 options page:

chrome_style (boolean) - optional

If true, a Chrome user agent stylesheet will be applied to your options page. The default value is false, but we recommend you enable it for a consistent UI with Chrome.

Is that stylesheet a stable API?

Where is that stylesheet?

Answer 1

I found the answer in Chromium source. The following two stylesheets are added to Options Pages with chrome_style:true:

• extension.css: https://chromium.googlesource.com/chromium/src/+/master/extensions/renderer/resources/extension.css
• extension_fonts.css: https://chromium.googlesource.com/chromium/src/+/master/extensions/renderer/resources/extension_fonts.css