If you want to offer as smooth experience to mobile user as possible, you want to match the theme of login screen with the theme of rest of the application.

In case of Ionic application, it will be Ionic style.

The problem comes with the approach that makes Keycloak authentication possible:

• it opens InAppBrowser (think of new window) where it displays mobile-optimized, but keycloak-styled login screen
• even if we restyle that, the keycloak template won't be as fast as possible since it first makes the request for particular HTML source and then requests CSS styles (that even imports other CSS files)

In order to make Ionic users happier, we can provide them Keycloak interface with Ionic styling out of the box and also make the user experience smoother by optimizing stylesheet loading.