how to center my theme ?

Hi everyone so I’m using the “store” theme for e commerce but I’d like to center everything that’s not the shop. Pages basically I’ve looked up how to do this and from what I understand I go to my style sheet and change the values in the base however there’s no base only “alignments” I tried changing everything there to math the center alignment but nothing changed on my site. if someone could tell me how to do this I’d appreciate it, cheers