Opacity lost in epub preview
I'm making this e-book on InDesign 2020.
The image is in Chinese but the items numbered ①~⑤ are set as buttons and are suppose to be 50% opacity until the mouse cursor hovers above it, so ②~⑤ were suppose to be 50% opacity while ① is 100%. But in preview, all of them show as 100%, same when exported.
Have tried changing the object style export options to rasterize container/ format png, but has no effect. Can someone help me with this, please?

