docs: def css(app, env):
      """
      Add bolditalic CSS.
  
      :param app: Sphinx application context.
      :param env: Sphinx environment context.
      """
      srcdir = os.path.abspath(os.path.dirname(__file__))
      cssfile = 'bolditalic.css'
      csspath = os.path.join(srcdir, cssfile)
      buildpath = os.path.join(app.outdir, '_static')
      try:
          os.makedirs(buildpath)
      except OSError:
          if not os.path.isdir(buildpath):
              raise
      copy(csspath, buildpath)
      app.add_stylesheet(cssfile)
      return