Not the reply I was expecting as I assumed it was a bug. My bad. Nevertheless a simple, straightforward solution that works – Thanks very much indeed @lorro
BTW, anyone using the Mystile theme will find that custom css entered at
Dashboard > Appearance > Customise > Additional CSS
gets overridden by custom css entered at the theme’s settings page. To get this to work with Mystile, paste the custom css at
Dashboard > Mystile > Settings > General Settings
Just scroll down to find the custom css box.