[X_TREME theme] How to fix the width size of the album frame?

Hello,

I am using the x_treme theme on my website www.parfumessence.fr and I am wondering how to fix the width size of the album frame?
Indeed the width of my album frame is actually dependant of the number of thumbnails I have per line and the more thumbnails an album contains, the larger the frame is but I would like the frame to be fixed to the maximum width. Do you know how to do it?

Also for the horizontal aligment of the thumbnails : I would like to align center the thumbnails (between portrait and landscape format). If somebody knows...

Thank you for your help