A complex page with flashing ads and content is generated by the server especially for the browser that visits. Javascript is the only universal scripting possible across all browsers and to make pages uniform CMS -- Content Management Systems is a variety of tiered-software. A database contains the content, a layer of management software such as AJAX, Joomla!, or POJO is programmed to interact between the visitor and the stored content.
Thus, you need to know javascript, CSS, html, dhtml, xml but I can't imagine any human-coded page being more than 300-lines of code max. Dreamweaver is nothing but grief.