inner method
Implementation
Rect inner(Rect area) {
final hasT = sides.hasTop ? 1 : 0;
final hasB = sides.hasBottom ? 1 : 0;
final hasL = sides.hasLeft ? 1 : 0;
final hasR = sides.hasRight ? 1 : 0;
return area.inset(top: hasT, bottom: hasB, left: hasL, right: hasR);
}