Customizing the button style is done differently depending on the JS framework you use.

Change the button to light mode by setting theme as light. Default is dark.

Customizing the button UI in React

Add custom styles to the CrossmintPayButton component using CSS. See the example of the React SDK below and note the className attribute:

import { CrossmintPayButton } from "@crossmint/client-sdk-react-ui";

export default function Mint() {
  return (
    <div>
      <CrossmintPayButton
        projectId="_YOUR_PROJECT_ID_"
        collectionId="_YOUR_CLIENT_ID"
        className="xmint-btn"
      />
    </div>
  );
}