It seems to be a Cache issue at your end because as we are visiting your Site, the Add to Cart button is showing in Red Color: https://snipboard.io/tBL4gv.jpg
Please check back your Site after completely clearing browser and server cache.
Actually it cause because of Plugin called ” WooCommerce Affiliate Automatic Amazon WordPress Plugin AMS” because it generated it own Add to cart button. So the issue gone after removing that Plugin.