Could use a little CSS help here, please….

On our woocommerce site: https://fishybusinessaquatics.com I have attempted to change the add to cart button as follows:

.button.single_add_to_cart_button.button.alt {
	background-color:#D51D29 !important;
	font-weight: bold !important;
}

on this page – https://fishybusinessaquatics.com/shop/invertebrates/white-shell-blue-leg-hermit-crab/ you can see it’s correct, but if you click it, then it turns back to the theme color, but not sure why.

On this page – https://fishybusinessaquatics.com/shop/corals/nano-brain-coral/ I can’t seem to get it to turn red at all, even when an item is selected.

Any insight on what I have missed?

Thanks!