.bird {
          position: absolute;
          left: -60px;
          width: 35px;
          animation: flyAcross 25s linear infinite;
          animation-delay: -1.5s;
        }

        @keyframes flyAcross {
          from {
            transform: translateX(0);
          }

          to {
            transform: translateX(calc(100vw + 80px));
          }
        }