srsly tho what is this friggin vertical rectangle called

what kind of css script do i need 2 add it 2 mah website fella.,,.,..,,.,.

like what is it this website obv has it you are seing it rn

most websites on neocities have it as far as ah c i needz hlep11!!!!!1

EDIT:wait hold on i think its called center!!!!!!!!!!!!!!!