LibreTube/app/src/main/res/drawable/ic_fullscreen.xml

<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="24dp"
    android:height="24dp"
    android:tint="?android:attr/colorControlNormal"
    android:viewportWidth="24"
    android:viewportHeight="24">
    <path
        android:fillColor="@android:color/white"
        android:pathData="M7,14L5,14v5h5v-2L7,17v-3zM5,10h2L7,7h3L10,5L5,5v5zM17,17h-3v2h5v-5h-2v3zM14,5v2h3v3h2L19,5h-5z" />
</vector>