@Andre, I have been unable to reply for some 5 hours now because the reply button is not functioning. I'm not having trouble with any other sites, so I assume that the server is very busy or down for some reason. I pushed the Publish button and got an editing screen.
You were quite right that I had the notebook magnification set at 150 and that was the problem. I changed it to 100 and the cdf files are all working well now except for an occasional thin white line at the bottom, but I can live with that. Many thanks for sticking with this to the solution. I will just put this together now so that the next person with this question can find it quickly:
My CDF manipulate programs were not displaying properly on the web. White panels were showing between the CDF frame and the web page background.
One should set the size somewhere in the script by including ImageSize --> N (a number) for a fixed size image or ImageSize --> Medium for an image that will resize as the web page is resized. Other possibilities are illustrated in the documentation for ImageSize. Places where one might set the image size include the options of Graphics[], Plot[], or Manipulate[]. I found that setting the size in Manipulate worked, but ImageSize printed Red, suggesting that it doesn't belong in the Manipulate options.
If one wants a colored background for the CDF that matches the background of the web page, that background has to be set in Format --> Background Color. Select the output cell first.
Before exporting, magnification for the web page should be set at 100 percent using Window --> Magnification. If this is not set, the actual size will not match that specified by the CDF Export wizard. I commonly use 150 or even 200 percent for editing, so I have to watch this.
In the source code for the web page where the CDF will be displayed, the bounding box should reflect the height and width given by the Export --> Web Embeddable wizard.