In my day-to-day work with Mathematica I use a stylesheet I have derived from Mathematica's default stylesheet. One modification I would like to make to my stylesheet is to reduce the spacing between a section title and the first cell inside the section. This is not controlled by the CellMargins option. Is there another notebook option that can be set to reduce this gap?
As commented by Mike Honeychurch:
The spacing is controlled by the cell margin.Try this:
Bear in mind that the total spacing between a section cell and the next cell is the sum of the bottom margin for the section cell and the top margin for the subsequent cell.
For a consistent spacing you will need to have the same cell type (e.g. subsection) following your section cell because most cells types are configured by default to have different top margins. (and therefore the spacing between section->input will be different from section->text etc.)