I got it, tweaking the code just a little. The code below adds an icon to any link to a page in the "members:" category:
a[href ^='/members:'] { padding-right: 18px; background: transparent url(/local--files/system:icons/members.png) no-repeat center right; }
Now, if I understand well, there should be a away of avoiding the code to apply to a given area, by creating a class canceling the code above. How can I do that, anyone?
Thanks for any tips!