Signal-Android/app/src/main/res/drawable/ic_add_members_circle.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="oval">
            <solid android:color="@color/core_grey_02" />
        </shape>
    </item>
    <item
        android:bottom="12dp"
        android:drawable="@drawable/ic_add_members_20"
        android:left="12dp"
        android:right="12dp"
        android:top="12dp" />
</layer-list>