code: def write_head(self, title, css_path, default_css):
          
          self.title = title
          self.write(
              '''<!DOCTYPE html>
  <html>
  <head>
      <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
      <title>{title}</title>
      <meta name="viewport" content="width=device-width, initial-scale=1.0">
      <link id="style" href="{rel_css}/docs.dark.css" rel="stylesheet">
      <script>
      document.getElementById("style").href = "{rel_css}/docs."
          + (localStorage.getItem("theme") || "{def_css}")
          + ".css";
      </script>
      <link href="https://fonts.googleapis.com/css?family=Nunito|Source+Code+Pro"
            rel="stylesheet">
  </head>
  <body>
  <div id="main_div">''',
              title=title,
              rel_css=self._rel(css_path),
              def_css=default_css
          )
docs: Writes the head part for the generated document,
             with the given title and CSS