Gadgetbridge/app/src/main/res/layout/activity_controlcenter.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="nodomain.freeyourgadget.gadgetbridge.ControlCenter">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="connect"
        android:id="@+id/startServiceButton"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentEnd="true" />

</RelativeLayout>