Add this custom CSS to the DIVI theme menu and see a new CSS style on WooCommerce product page.

woocommerce input.button:hover, .woocommerce-page input.button:hover,
a.checkout-button.button.alt.wc-forward:hover {
padding: 10.2px !important;
color: #fff;
}
.woocommerce-message a.button.wc-forward {
background: #ffffff;
font-family: 'Nunito';
font-size: 16px!important;
color: #424242;
}
input#coupon_code {
background: #424242 !important;
font-family: 'Nunito';
font-size: 16px!important;
}
.woocommerce input.button, .woocommerce-page input.button,
a.checkout-button.button.alt.wc-forward {
background: #e02b20;
font-family: 'Nunito';
font-size: 16px!important;
color: #fff;
padding: 10.2px !important;
}