You can see the last iteration of the ​new style here.

Some of the new features:

• Validated XHTML 1.1 output (better than strict XHTML)
• New header and footer based on beta.boost.org.
• ​GroupedLinks select boxes for Boost Libraries and Section quick jumping.
• Google Search box over our docs.
• Box-wrapper based blurbs that allow us to include rounded corners, drop shadows, etc.
• Alternatives syntax highlighthing that simulates your own IDE (move the mouse to the upper-right corner of a code block)
• Chapter logo support
• Modular css design
• css based admonitions and navigation graphics
• Quickbook source stylesheet
• PDF stylesheet matches the HTML style.

You are welcome to join ​boost-docs list to help us improve it even further.

The project is hosted in boost sandbox at boost/sandbox/doc_test

Last version of Boostbook: boost/sandbox/doc_test/box_wrapper/xsl