private void AnimateTabPageOpen()
        {
            var animation = new DoubleAnimation();

            animation.From     = 0;
            animation.To       = 1;
            animation.Duration = new Duration(TimeSpan.FromMilliseconds(TAB_PAGE_OPEN_ANIMATION_TIME));

            var ease = new CubicEase();

            ease.EasingMode = EasingMode.EaseIn;

            animation.EasingFunction = ease;
            CurrentPage_CONTENT.BeginAnimation(OpacityProperty, animation);
        }
        private void AnimateTabPageClose()
        {
            var animation = new DoubleAnimation();

            animation.From       = 1;
            animation.To         = 0;
            animation.Completed += AnimateTabPageClose_Completed;
            animation.Duration   = new Duration(TimeSpan.FromMilliseconds(TAB_PAGE_CLOSE_ANIMATION_TIME));

            var ease = new CubicEase();

            ease.EasingMode = EasingMode.EaseOut;

            animation.EasingFunction = ease;
            CurrentPage_CONTENT.BeginAnimation(OpacityProperty, animation);
        }