Thanks guys for your assistance, during this frustrating period.
In brief, to answer your questions:
1, Chrome, Firefox, Microsoft Edge were all the latest versions and all had the same problem.
2. Both widescreen monitors are fairly new and are calibrated with a Datacolor Spyder for photo editing and printing, i.e "WYSIWYG" (What You See is What you Get). From the calibration, viewing of the end result by eye and test prints, it is assumed that the brightness and contrast and colour calibration are about as close as I am going to get them.
3. Graphics Card was up to date with latest drivers.
4. I subscribe to a number of forums and spend a lot of time on the internet and no problems with any other site or forum.
5. I had my annual eye test yesterday and ruled out things like macular degeneration.
Horse, you are a legend. Whatever magic you conjured up with the "Default Style" worked a treat! I can now see things clearly. Thank you so much.
Cheers, Gary