Hi Kristóf,
Greetings from Syncfusion support.
We considered the reported issue (“Outline theme border bottom issue”) as a bug at our end. We will include the fix for the reported issue in the Volume 1 main release which is expected to be rolled on March 17th,2021 . We appreciate your patience until then.
You can track the status of the reported issue from the below feedback link.
Regards,
Sevvandhi N