If you generally like one of the existing templates available, you can simply style that template using the built-in customization features (colors and logo) available in the Premium subscription as well as additional CSS styling that you add. See Configuration-of-the-Swift-banner
If you want to build a custom banner, you will need to apply your own coding logic in order to do so. The ‘custom’ template has HTML placeholders and naming conventions that can help you do this. They are available from the little question marks on the custom template.
[#DETAILS#] will give you the desired show/hide details label.
The custom banner will use the fields on the Dialog tab from the banner type that you had selected before changing to Custom.
It is recommended to select a banner that comes closest to how you want your custom banner to behave before changing to custom.
You can find instructions including more information about what is provided as a basis that will help you build your custom banner: Can-I-build-my-own-fully-customized-cookie-consent-banner