.birds{position:absolute;left:0;right:0;top:15%;height:200px;pointer-events:none}
.bird{position:absolute;width:56px;height:28px;transform-origin:28px 14px;animation:birdFly 16s linear infinite}
.bird:before,.bird:after{content:"";position:absolute;width:24px;height:8px;background:transparent;border-top:5px solid #222;border-radius:50%;transform-origin:12px 4px}
.bird:before{transform:translate(0,6px) rotate(-18deg);animation:wingFlap 0.6s ease-in-out infinite}
.bird:after{transform:translate(28px,6px) rotate(18deg);animation:wingFlapRev 0.6s ease-in-out infinite}
.b1{left:-10%;top:35%;animation-delay:0s}
.b2{left:-20%;top:22%;animation-delay:2s}
.b3{left:-5%;top:50%;animation-delay:4s}
@keyframes birdFly{
  0%{transform:translateX(-20vw) translateY(0) rotate(0) scale(0.95)}
  30%{transform:translateX(30vw) translateY(-4vh) rotate(-6deg) scale(1)}
  60%{transform:translateX(70vw) translateY(-10vh) rotate(6deg) scale(1)}
  100%{transform:translateX(140vw) translateY(0) rotate(0) scale(0.95)}
}
@keyframes wingFlap{0%{transform:translate(0,6px) rotate(-18deg)}50%{transform:translate(0,2px) rotate(-40deg)}100%{transform:translate(0,6px) rotate(-18deg)}}
@keyframes wingFlapRev{0%{transform:translate(28px,6px) rotate(18deg)}50%{transform:translate(28px,2px) rotate(40deg)}100%{transform:translate(28px,6px) rotate(18deg)}}