For anyone who will probably have same problem but have people like @jabaa say their question sucks instead of being truly helpful people, the issue was that the text decorations were only highlighting on the original text and not on the diff text itself since i haven't added the diff text to the file in the editor, so the fix is simply to make sure you add the diff into the file but hold context to the old text incase the user rejects the changes so you can reverse it back to the original text.