crossoriginstylesheets

Crossoriginstylesheets refers to the use of the crossorigin attribute on link elements that load CSS from a different origin than the current document. This approach governs how the browser fetches the stylesheet and how associated cross-origin resources are treated. The attribute accepts the values anonymous or use-credentials.

When a cross-origin stylesheet is requested with crossorigin="anonymous", the browser performs a CORS request without credentials such as cookies or HTTP authentication data. If the attribute is set to use-credentials, the request includes credentials. The presence and value of this attribute influence what types of resources referenced within the CSS can be loaded and how they are permitted to be used by the page.

Cross-origin stylesheets interact with other cross-origin resources, notably fonts and images referenced by the CSS via @font-face or background URLs. For these resources, the server hosting them must permit cross-origin access by sending appropriate CORS headers (for example, Access-Control-Allow-Origin). Without proper headers, fonts or images loaded from a different origin may be blocked or cause rendering issues, even if the CSS file itself loads successfully.

Best practices typically favor using crossorigin="anonymous" for public CSS resources served from CDNs, unless there is a specific need to send credentials. Developers should ensure that all cross-origin resources required by the stylesheet are properly configured to allow cross-origin access. Security and privacy considerations include the potential exposure of user data when credentials are sent to third-party origins.

Browser support for the crossorigin attribute on link elements is widespread in modern browsers; however, behavior may vary if servers do not implement correct CORS responses.