MyActivity.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/intro_app_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/intro_app_name"
        android:layout_marginTop="8dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"/>

    <RadioGroup
        android:id="@+id/intro_level_selector"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@id/intro_app_name"
        app:layout_constraintBottom_toTopOf="@id/intro_rv">

        <RadioButton
            android:id="@+id/selector_level_easy"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:background="@drawable/level_select_button"
            android:text="Easy" />

        <RadioButton
            android:id="@+id/selector_level_medium"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginStart="15dp"
            android:gravity="center"
            android:background="@drawable/level_select_button"
            android:text="Medium" />

        <RadioButton
            android:id="@+id/selector_level_hard"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginStart="15dp"
            android:gravity="center"
            android:background="@drawable/level_select_button"
            android:text="Hard" />
    </RadioGroup>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/intro_rv"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toBottomOf="@+id/intro_level_selector"/>

</androidx.constraintlayout.widget.ConstraintLayout>