Carbon theme customization

Hi,

I'm currently using the carbon theme. I have 2 problems :

1. I would like to change the spacing between my pictures thumbnails. I guess it has something to do with a padding parameter but I can't find which line to modify in the carbon theme.css file.
For horizontal spacing, it's probably calculated automatically by the the total width and number of thumbnails ona line/size of thumbnails. But for the vertical spacing, I would like to do it minimum...

2. I've found that the thumbnails automatically generated have been compressed with a very poor quality. Can I change it ? If not, where are the thumbnails generated located (I can replace them manually)

Thank you