I’m not sure where exactly this behavior comes from but it didn’t affect our old editor (non-ProseMirror).
This is the browser’s native behavior (you’ll see the same when dragging something outside of the editor). I’m not sure there’s any way to improve it.
Interestingly our current editor (built with Slate 0.46) does not exhibit this behavior. It drags with a transparent background. As far as I know if doesn’t have any special logic for this, it “just works.” Unfortunately it working by apparent magic makes it quite difficult to make the same behavior occur in ProseMirror.
But in a sandbox Slate has this behavior too… I can’t imagine what the secret sauce is in our current editor that avoids this problem.
Ah I see the distinction is at the OS-level. Linux = ugly white blocks. Windows = transparent text selections.