When you are done customising your sign and click "Add to cart" you may be wondering why it takes about 4 seconds for the product to be added in the cart.
When the "Add to cart" button is clicked we have to perform a number of steps before it can be added to the cart in the users browser:
Images are generated for the product page and the cart preview
The preview images and any custom images uploaded by the user must then be uploaded to our servers
We then need to create the product in your store with all of the required details and then upload the images there once more
Products are not necessarily available immediately upon creation so we need to wait until it appears in your store before finally adding it into the cart
This whole process usually takes 4 - 5 seconds in Shopify environments to complete which is why you see the loading screen after clicking "Add to cart".