CustomAnimation.dart

CustomAnimation(
              tween: Tween(begin: 0.0, end: (_screenWidth * 0.8) / 2),
              duration: widget.animationDuration,
              curve: Curves.easeOut,
              control: _control,
              builder: (context, child, value) {
                return Padding(
                  padding: EdgeInsets.only(left: value),
                  child: Container(
                    width: value <= ((_screenWidth * 0.8) / 2) / 2
                        ? (value + ((_screenWidth * 0.8) / 2))
                        : (_screenWidth * 0.8) - value,
                    height: 50.0,
                    margin: EdgeInsets.all(5.0),
                    decoration: BoxDecoration(
                      borderRadius: BorderRadius.circular(100.0),
                      color: Colors.white.withOpacity(0.4),
                    ),
                  ),
                );
              },
            )