[GeoffR]

If you want the top margin 25px and bottom margin zero, just enable the patch and don't change anything else, the example already sets the margin to 25px.

But in general:

1. Select one of the alternatives by uncommenting one and commenting out the other, but don't edit these lines otherwise.

2. Set the margin size by changing the replacement value in the last line of the patch. The margin size you set in the last line applies to both alternatives. The example changes the initial value from 10px to 25px.