Why the WEBGUI is not displaying my custom theme?

Warning! This is a hypothetical tale, but can be true nightmare history for some readers…

I have a Portal, with my company’s visual identity defined via a custom theme. A custom font was used as new developed icons. For all screen elements/components, a specific color was chosen.

I created a Transactional iView, to display HCM data in the Portal. Everything was working fine, the custom theme was being used in the Portal and in the ECC… until my Basis team patched the kernel of the ECC system. Now I see the Portal using the custom theme, but the iView uses a SAP theme.

Why this is happening? How to fix the issue?

I learned, after reading some SAP notes, that the CSS version from the Portal and the ECC must be compatible, so my custom theme can be used.

I found SAP note 1802264, that tells about the CSS version (or, in SAP terminology, UR version) available in every single patch kernel.

I compared the CSS version from the ECC with the one from the Portal. I discovered that my Portal components needed to be updated to restore the compatibility. I followed the steps from SAP note 1446099 and resolved this issue.

The bottom line is that, whenever the ECC kernel is updated, I need to check both SAP notes, so the look and feel is not broken when the Portal is accessed.