2012 Nuevo Ceiling light - Changing Bulb

Although I don't have a problem at present I would like to know how to get the cover off the ceiling lights to replace the "bulb". 
The unit is circular with a frosted acrylic dome set in a chromed plastic surround with the switch.  All the other lights in the van are LED's.  This may be LED or possibly some other form of energy saver.  I can see no way of getting in and there seems to be no give at all on the cover or any indentations to allow it to be prised off.

There is a similar light over the sink which is oval rather than circular which might be the easier one to try first once I have some idea of the knack.

I imagine that all the modern (2012 on) coachbuilts have the same units.

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