PDF -> Mobi: Remove underline from links

Hi everybody,

I would like to remove the underline from links when converting a pdf to mobi. So far I could specify my own custom css when doing the convertion using:

However, when opening the mobi file in calibre the links are black but still underlined. I discovered using the Inspector that for this underline the "user agent stylesheet" is responsible. How can I change this "user agent stylesheet" css and make that links are no longer underlined.

Best
Andy