As per ui@5.1.2, a selected prop was provided to the custom options to enable specific styling for the right side items. However, as per the latest ui release (ui@5.5.0 at the time of writing), this prop isn't provided anymore.
Currently, the demo for custom options looks like this (screenshot below), which doesn't include the orange styling for the right side (as the selected prop isn't provided anymore.

Compared to 5.1.2:

Live example here: https://codesandbox.io/s/ui5-transfer-right-side-style-bkgrc
Change the dependency to 5.5.0 to see the difference in the styling.
This creates a bug in DHIS2-8807 which is due to be released for 2.35 (soft freeze 25/8)
As per ui@5.1.2, a
selectedprop was provided to the custom options to enable specific styling for the right side items. However, as per the latest ui release (ui@5.5.0 at the time of writing), this prop isn't provided anymore.Currently, the demo for custom options looks like this (screenshot below), which doesn't include the orange styling for the right side (as the selected prop isn't provided anymore.

Compared to 5.1.2:

Live example here: https://codesandbox.io/s/ui5-transfer-right-side-style-bkgrc
Change the dependency to 5.5.0 to see the difference in the styling.
This creates a bug in DHIS2-8807 which is due to be released for 2.35 (soft freeze 25/8)