One image is worth a hundred speeches
Thanks Jacques for reporting the issue, I am able to replicate it and will provide a patch soon to fix the issue.
Hi Jacques Le Roux,
I have added the missing CSS styles for Rainbow theme in themes/rainbowstone/webapp/rainbowstone/style.css to improve the rendering of the list of visual themes also attached a screenshot for your quick reference.
I have attached patch for both trunk and release16.11.
Your patch is in
FYI: you did not need to provide a R16 patch, it was easy to automatically backport.