Templates in zencart are constructed using PHP, and the code conforms to the core zencart structure. The LAYOUT of these templates is then influenced by CSS, where the declarations are dependent on Style ID's and Classes that are embedded in the PHP code.

So... ZC templates are styled using CSS, but the pages are built using PHP.

It is therefore not possible to use these free css templates, but you may possibly get some ideas that you can embody into your ZC layout & design.