The other day I was modifying a file, and I accidentally caused this GUI modification
The required Look and Feel was the one on the left, where all balls are one beside the other.
What I did was wrap those circles with an HBox.
It was obvious to me that I needed a behavior similar to border-collapse for a table or some sort of padding in CSS - as shown in this table style wizard.
The answer to my question was "horizontalGap". Setting this to 0, gave me the required behavior.