Fixed multiple bugs

【Contents of fixes】
■Support for mobile friendly testing.
■Fixed a bug that the slider on the product (custom post) page does not show up when eye catching is not set.
■Fixed a bug that the slider on the product (custom post) page does not show the eye catcher or the first image after “Slider Image 2” when “Slider Image 1” is not set.

The following are the files that have been modified for this update.
【Corrected files】
・css/responsive.css
・single-cpt.php
・style.css