function _computeCenterX( element ) {

	const padding = element._padding._value;
	const borderWidth = element._borderWidth._value;

	const leftSide = padding.w + borderWidth.w;
	const rightSide = padding.y + borderWidth.y;

	return ( leftSide - rightSide ) / 2;
}
Retrieve the center X according to box sized dimensions
@param {MeshUIBaseElement} element
@return {number}