Custom CSS is divided into two general options, the preconfigured color schemes, following the root params will affect multiple sections of the payment page design.
The second option is adding specific CSS classes that appears in the code to overrun on the built-in CSS class, to check the CSS class simply "inspect element" in the browser.

To configure the text go to the Payment Page Settings page on our MCP and go to "CSS" - you can add additional languages and enter the text in the first box.

The below code will give you the abiiity to update the params across the CSS file, be sure to include all the params.

:root {
--GatewayBorderColor: #aaa;
--GatewayMainColor: #8dc059;
--GatewayMainColorHover: #578623;
//Hide buttons - set to "none" in order to hide them on the payment page
--GatewayShowEdit: initial;
--GatewayShowBack: initial;
--GatewayPaymentMethods: initial;
}