First of all, thank you for developing and sharing this add-on.
I've noticed that the add-on works correctly only for the administrator group. For other user groups (such as moderators or custom groups), only the username color is applied — the style (e.g., bold, italic) does not appear to take effect.
Additionally, this issue also affects thread starter posts — the style is not visible in the first post of a thread, but it does show correctly in replies made by the same user.
Could you please take a look at this when possible?