Joomla 3.0 is shipped with a LESS files located in
media/jui/less/ to generate default template and bootstrap CSS files from LESS files.
The CSS generation wrapper script, LESS compiler, and other similar build tools are located in the build directory. The build directory is only available from a GitHub clone; it is not included in an official Joomla release.
To generate the CSS files you will need to execute the generation scripts as a CLI application.