Spacing between Group Controls with Header and Border 

Group controls with header and border should also be surrounded by a 10 pixel offset to clearly separate the single groups from each other.

Spacing group controls with header and border

A smaller offset makes the area around the borders noisy and disquiet. When more then two borders come together in a very small space it is very hard to figure out which border belongs to which group. It becomes even harder, when the borders have the same color.

Example of noisy interface