Android Studio – Android RadioButton button not appearing in editor

Here is my activity_main.xml :

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="@android:color/white">
    <include layout="@layout/toolbar"></include>

    <RadioGroup
        android:id="@+id/choixPersonnage"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <RadioButton
            android:id="@+id/boutonGuerrier"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/personnage1"
            android:textSize="20sp"/>

        <RadioButton
            android:id="@+id/boutonMage"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/personnage2"
            android:textSize="20sp"/>
    </RadioGroup>

</LinearLayout>

And here is what appears in my editor:

Both button texts work, but the RadioButton buttons just do not appear, nor do they take space. They are just not there…

In all the Radio Button problems I found, no one seemed to have the same problem I do. Anyone could help me out here with this basic thing?