You can style your Identity Management templates via the CSS tab in the Piano ID Layout template.
If you want to distinguish Identity Management templates that are being opened via checkout from Identity Management templates that are being opened directly e.g. via tp.pianoId.show(), you can use the classes .piano-id-inline(checkout) and .piano-id-modal (directly opened) in your Piano ID Layout template's CSS tab to do so.
For example, if you want to have red text in your Identity Management template (on the login and registration screen) when opened from checkout and green text when opened directly, you would add the CSS like this:
.piano-id-inline { color: red;}
.piano-id-modal {color: green;}