Sam,  Yes that did correct the issue...   A space made all the difference.  Thank  you.

Now for my next challenge....   I have a module.css  that could be used in either the darkbackground or Lightbackground.  The module generates a grid and I would like the grid header to have a light background on the DarkBackground container and a darkbackground on the lightBackground container.  Rather standard stuff I believe.  So where is the appropriate location to implement the classes.  It seems that the Module.css is declared before the container.css.  I believe the order is significant and may cause some difficulty.   So I will end up with:

Container.css

.darkbackground .gridheader { color:black; background:white; ...}
.lightbackground .gridheader { color:white background:black ; ...}

module.css

.gridheader { font-family: Tahoma, Arial, Helvetica;  font-size: 11px;  font-weight: bold; }

OK so far?  This seems to work.

Well the grid allows sorting so, the header must handle link, visited, active and hover.   This too will be conditional on the background class - so how does that work as the following does not  

.lightbackground  a.gridheader:hover { color: yellow; }

Any help would be appreciated.

Sam ... as the saying goes .. "you ARE the man!"

I took your suggestion and used  ( colors are for testing - final colors will be used when all is working as needed)

.darkbackground a:link       { color: white;  text-decoration: none; }
.darkbackground a:visited { color: yellow; text-decoration: none; }
.darkbackground a:hover   { color: red;    text-decoration: none; }
.darkbackground a:active  { color: red;    text-decoration: underline; }

Works like a charm ... many many thanks .