Subtitle extracting problem with MKV

Hello, there's this one subtitles I want to add to my own DVD rip. The subtitles come from fansub source. I want to extract the .ass and mergue it with MKVToolnix to get it on my own rip. I extract the subtitles with "MKVExtractGUI". It all goes well until I merge or open it with my own rip. The subtitles loses the styles and the original fonts and stuff and replaces them instead with an ugly default looking one.

What do I do to extract and mergue the subtitles to my rip exactly with the same styles, fonts, everything?


Thanks.