XF 1.2 Thread Prefix CSS not Updating in ACP

So I modified a load of my thread prefix CSS under a custom style, it shows fine when I select the prefix when creating a new thread. Issue is, I still see the default prefix CSS when in the ACP and managing thread prefixes.

How would I go about resolving this? Preferably without having to alter the default style's CSS as well. I presume it's because it's not using the CSS from my style for the ACP?