How to show caret and underline in SearchView-Widget (Android)

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I try to put a searchbar in the navigation of a content page on Xamarin.Forms (Android). I use the following from https://www.linkedin.com/pulse/xamarin-forms-contentpage-searchbar-navigation-bar-vipin-mathews.

However, if the user enters the SearchView no caret and no underline is shown:

I want to display something like this (without icons)