Google Sites relative to standard web technologies:

Purpose	Web Technology	Google Sites
Static Content	HTML	WYSIWYG editor creates HTML  HTML available to view and edit
Style / Presentation	CSS - Cascading Style Sheets	Select from Themes (many preconfigured)  Google interface to customize style settings  No direct access to site-wide CSS files*
Dynamic Content	JavaScript...	Google Apps Script - written using JavaScript and Google APIs,  then integrated into a site via a link or object  JavaScript cannot be directly written in a page's HTML*

* CSS files for the overall site cannot be viewed or edited. Within a standard page, inline <style> tags may be used. Sites also supports an HTML box object that can include CSS & JavaScript for use within that object.