Microsoft are retiring custom CSS positioning in company branding

This article details Microsoft's announcement (message ID MC1435782) to retire support for custom CSS positioning properties in company branding for Microsoft Entra ID, effective 26 October 2026. The change is part of the Secure Future Initiative (SFI) to tighten identity security and reduce phishing risks by enforcing a consistent, predictable sign-in page layout. Properties like position, margin, transform, opacity, and others will stop functioning, with no migration path provided. Organizations using custom CSS in branding must audit their stylesheets before the deadline. The article explains who is affected, including that tenants created after 5 January 2026 cannot use custom CSS at all. It offers guidance on preparing for the layout changes.