## Rules

The [`theme_rules`](/openapi/sale-request-examples/checkout_request#sale-request-examples/checkout_request/t=request&path=payment_form_override/theme_rules) option is a mapping of CSS-like selectors to CSS properties, enabling precise customization of individual components. Once you’ve defined your theme and variables, you can use these rules to seamlessly align the payment form with your website’s design.

Selectors in a rule can target any public class names within the payment form, as well as supported states, pseudo-classes, and pseudo-elements associated with each class. For example, the following are valid selectors: `.form-control > input`