Adding the CSS
The first step, which we’re not going to cover here, is to set a custom class called “custom-checkout” to your checkout shortcode. This is done differently depending on what theme you are using, so you will have to search around for this if you are unsure.
Next, it is time to add the following CSS to your website. If you are using Divi then you can do this in your “Theme Options” and “Custom CSS” section. If you are using another theme then you will probably have an option somewhere to add custom CSS to.