You can adjust the look of your form fields to fit your store’s theme using the App embed settings:
In your Shopify admin, go to Online Store > Themes.
Find your theme and click Customize.
Click the App embeds tab.
Beside Magical Custom Fields, click the expand icon.
Update the style settings as you like. Use the theme editor’s page selector to preview a product with custom fields before you publish the changes.
Click Save when you’re happy with how it looks.
This lets you keep your forms looking consistent with your brand and storefront.