Hi Rolf,
I looked at your website again just now, and the two customized files are still in place : on the product page the image block is still at the end of the right column, and in the category listing the product name is still displayed below the price and your delivery text. So the "Remove customization" step in Display > Views has not been done yet, and it is the only thing needed to get your original layout back.
About how it happened : the popup of the drag & drop editor saves a copy of the view file on your website as soon as you click Save, even when you have moved the blocks back to their original place first. Moving an element back does not delete that copy, it saves a new version of it, so the page keeps using the copy instead of the original file of HikaShop.
And on the product page, the image was not only moved up or down : it was dropped in the right hand column instead of the left one. That is why that page looks stretched, the left column is now empty and everything, the image included, is in the right column. It happens easily when the block is released a few pixels away from where you aimed.
About Astroid : yes, the Custom CSS field of your template is the correct place, what you write there ends up in the CSS file the template builds. The reason nothing happened is the CSS itself, not the place where you put it. The class hikashop_product_name_main only exists on the product page. In your category listing, the class of the product name is hikashop_product_name. This line covers both pages :
.hikashop_product_name a, .hikashop_product_name_main { font-weight: bold; }
I also checked the CSS your template delivers today, and it contains no rule at all about the product name, so nothing of what you tried before is left, you can paste this one on a clean slate. Save, then reload your page with Ctrl+F5. If you still see no change, tell me and I will look at the page.