Looks like the module is not installed in the site, because adding product to...

Looks like the module is not installed in the site, because adding product to cart causes a page reload. Also neither of the blocks provided by the module are placed on the site, you need either one of the block so that the CSS is loaded in the page.

Please refer the installation steps properly, they are mentioned here https://www.drupal.org/project/dc_ajax_add_cart under 7.x