The html and css to support horizontal navigation are already present in Web Site Software, they're just disabled by default. steps to enable top nav:

1. Click menu Tools, Options, Link

2. Enter title and URL, for example:

   Download=/download-websitesoftware/
   License=/websitesoftware-license/
   Buy Now!=/buy-websitesoftware/
   Contact=/send-us-feedback/
   

3. Click “Apply” button to save settings.