Feel free to set most of the store settings according to your preferences. However, the following settings will optimize some of the built-in design elements.
Under Setup & Tools > Store Settings > Display
Under Setup & Tools > Store Settings > Images
Some theme images (such as icons, arrows, etc.) on your Bigcommerce store are stored in a Master Folder on the server.
Editing your theme stylesheet or creating an images folder in template directory of your store will cause images load from that new folder. If the location doesn't contain all of the images, you will see image errors on your store.
Solution - The following support article explains how to upload the theme images to your local theme folder - https://support.bigcommerce.com/questions/905/Why+are+some+of+my+images+not+appearing+on+my+site%3F.