Important: #107420 - Relative URLs in inline CSS of f:asset.css are rewritten 

See forge#107420

Description 

The Fluid ViewHelper <f:asset.css> with the argument inline="1" embeds the content of a stylesheet file into the page. Relative paths in url() and @import statements of that file were previously kept as they are, which made them point to non-existing locations once the CSS was part of the HTML document.

The paths are now rewritten to the public location of the referenced resources, the same way it already happens for stylesheets added via page.includeCSS with inline = 1 .

Note that the referenced resources are now resolved. If a stylesheet contains a relative url() to a file that does not exist, a \TYPO3\CMS\Core\SystemResource\Exception\CanNotResolveSystemResourceException is thrown while rendering the page. Previously, such broken references were silently output as-is.

Integrators should make sure that all relative paths in inlined stylesheets point to existing files, or remove obsolete references from the CSS.