Apart from the basic settings of modifying your button, you can choose to go for Advanced Settings as well. This setting allows you to alter the quick buy button or the add to cart button.
To access the Advanced Button Settings, click on Customize > Theme Settings > Advanced Buttons.
Enable 'Free + Shipping' feature
The free+shipping is a strategy used to offer a product for free and make the client only pay for the shipping. Inside Booster Theme, you have the option to change your Add to cart button into a personalized Free+Shipping text, the theme will detect when the product is set to $0.
BUY NOW BUTTON (PRODUCT PAGE)
This setting allows you to choose between the Primary or Secondary button combo.
You can choose a button type for your Buy Now button.
This setting allows you to change the text size for your Buy Now button
With the help of this setting, you can modify the text of the Buy Now button into all Uppercase or all Lowercase.