Signal-Android/app/src/main/res/drawable/conversation_attachment_close_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">
            <size android:height="21dp" android:width="21dp"/>
            <solid android:color="@color/red_600"/>
            <stroke android:color="@android:color/transparent"
                    android:width="3dp"/>
        </shape>
    </item>
    <item>
        <bitmap android:src="@drawable/ic_clear_white_24dp"
                android:gravity="center" />
    </item>
</layer-list>