paypal checkout smart button becomes gray

Everything works perfect until I recently install the WPC Product Bundles 3.6.5 plugin. To test out the function of the plugin, I changed one of the Variable product into a Smart bundle. It is very strange that the Paypal checkout button of the Smart bundle listing is in grayish color but the same Paypal checkout button in all other product listing in my site is in color.

I tried to check the color of the button in Woocommerce setting but didn’t help. Is that a bug?

Elton

The page I need help with: [log in to see the link]