Hi Alvaro,
You need to add the custom CSS code into the Theme Options > CSS to override the default style in the Cart page only. Please change the color as per your need.
.woocommerce-cart .button
{
    background-color: #ff0000 !important;
}
Please remember that the above code will work if copied as it is and doesn’t conflict with any existing style.
Please note that the code provided serves only as a guide to help you get started custom coding on your own if there’s no option offered in our theme or the products we bundle.
We really do not provide support for custom codes that means we can’t fix it in case it conflicts with something on your site nor will we enhance it.
Thanks