When a style specifies a border the size of the border is added to the control when the style is applied e.g. a standard textfield is 100 x 22 would become 102 x 24 if a style with a 1px full border was applied. The IDE however doesn’t show this adjustment in the inspector. It’s not usually a problem because there is sufficient space between controls, but sometimes you want controls very close to each other and then you have to remember to add the style sizes to the control sizes.
The purpose of this conversation is to see if I should file a bug report (to get the actual size in the Inspector) or a feature request to show the impact of the style in the inspector (with perhaps a +2 next to the width & height) & layout window. A container control will show the effects of adding a style by displaying a scroll bar which prompts you to increase the size to accommodate the style, other controls not so much.