How to change font-size and Box width of "Add to cart" button

How do I change font-size and box size of “Add to cart” button.

Hi there,
Thanks for reaching out.
In relation to your question here, please try out the following CSS code under the Appearance>Customize>Additional CSS section:

button.single_add_to_cart_button.button.alt {
width: 200px !important;
font-size: 30px !important;
height: 90px !important;

You can alter the sizes to those of your preference.

I hope this helps.
Best Regards,