Threema-Android-mirror/app/src/main/res/drawable/ic_baseline_add_24.xml

<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:height="48dp"
    android:width="48dp"
    android:viewportHeight="24"
    android:viewportWidth="24">
    <path android:fillColor="@android:color/white" android:pathData="M19,13h-6v6h-2v-6H5v-2h6V5h2v6h6v2z"/>
</vector>