I think you're on the right track with modifying the CSS to modernize the current layout. I have used CMSs (Joomla! in particular) for non-tech clients in the

I think you're on the right track with modifying the CSS to modernize the current layout. I have used CMSs (Joomla! in particular) for non-tech clients in the past, and it was always too much for the client to handle just for creating and posting new content. They ended up relying on me or some other developer resource for updates in the end. The one exception might be WordPress, but even that might be too much for the non-techie client. I would recommend creating a basic, homegrown CMS using a framework like Django, or ASP.Net Web Forms that gives your customer exactly what they need and nothing more. The up-front cost to the client is probably more than going with a traditional CMS, but likely to be cheaper in the long-run in terms of support.