If you're using HTML render kits for JSF, then yes you should probably
use CSS to work with the visual appearance of the page.  The HTML render
kit tags have attributes that can be used to apply classes or CSS styles
to JSF controls.

Tiles is a framework created by David Geary for doing layout of JSP
pages.  It is organized around writing JSP pages that represent pieces
of the page (for example, a header, or a menu to go in the left margin),
and then another JSP page to put them all together.  It has some
advantages in terms of modularity versus duplicating the content across
several pages.  I consider Tiles mostly a legacy technology these days,
though, since the same thing is easier to accomplish -- and introduces
no extra third-party software dependency -- using JSP tag files in
recent versions of JSP.

Tiles does not create any additional layout options versus plain HTML.  
Its purpose is to avoid duplication, not to add presentation options.