This is to update the Sphinx themes of various DM sites to use the new Rubin Observatory and Legacy Survey of Space and Time (LSST) branding guidelines at https://project.lsst.org/documents/name-use-guide/visuals

Specific projects are:

• https://github.com/lsst-sqre/lsst-sphinx-bootstrap-theme (applies to most software documentation sites)
• https://github.com/lsst-sqre/lsst_dd_rtd_theme (applies to most technotes)

Also ensure that these sites are updated, which don't directly use any of the other themes:

• https://developer.lsst.io