Thanks for the answer, kronos. I’m not sure if I understood this (sorry).
If I create a custom css, and I import it from epik’s style.css, I have to set the “@import custom.css” at the beginning, and thus my modifications are overriden by epik’s css.
I have tried moving the original epik’s css to another css and importing it, but it doesn’t seem to work well, somehow it seems to lose all layout information.