In navbar at Cart button, there is Clear Cart button.
The work of Clear Cart button is to clear the Cart. But it is not working.
Update clearCart funtion in index.html file of shop.
If you click on Add to Cart button, it will add the product in your cart and converts itself into plus and minus button.
As you click on plus button it will increase quantity of product in your cart and if you click on minus, it will decrease quantity of product in your cart.
After clicking on plus and minus button, when there is product quantity 0, this button again converts itself into Add to Cart button.
But after that it is not working. It will not add the product in your cart again.