Uh,
just received request to change just for one page CSS elements (like h1, h2,…). No matter how easy that looks it is not.
Fortunately there is module named CSS Injector (drupal.org/project/css_injector) that fix exactly what I needed.
Just install it, and go to configuration. Add new rule (call it by your page name, for example), add new CSS rules and select to be
visible only for a given node.

Thanks Eaton (@eaton)
all done.