Thanks for the suggestions, ladies. Hilary, the form already was in color, that's why the whitespace was so annoying. Doreen, I clicked each section on the form and on the "Control Tools" ribbon "Properties" tab I checked everything. The bottom margin was set to 0 px and the other three said "Auto". I changed all of them to 0, no difference. I changed all of them to auto, no difference. I also realized I also have two sections that are never hidden with nothing in between and yet there is always one pixel row between the sections. I have editted the xsl file and changed all occurrences of 1px to 0 px, to 10 px, to -1px, 1pt to 0 pt, 10pt, etc., changed all occurrences of transparent to black, white to black, #ffffff to #000000, many many changes, too numerous to remember, let alone mention. That one pixel row between each section would not go away. Then I realized my problem. I had put each section inside a table cell. Even though the table was only one column wide so when I hid a section I was emptying the whole row. I guess it still needed to be represented somehow. If you leave a row in a table empty you still can't set the row height to less than 4, so I am surprised that I didn't have that much gap for each row.
Basically, I was converting an Excel spreadsheet to a form we could implement on SharePoint. It had one sheet as a form and one sheet of instructions. I was putting it all in a single form with the instructions hidden unless you click a little button. I started with a table with one column and 16 rows. In each row I put a section and in each section a table containing a portion of the cells of the spreadsheets.
I simply cut each section from the table it was in and pasted it outside the table, one after the other and everything looks good now.