採用LP作成

https://baigie.me/officialblog/2021/02/25/css-tips-1/

鳥が飛ぶHTML

<div class="bird"></div>
<div class="bird -type_2"></div>
<div class="bird -type_3"></div>

鳥が飛ぶcss

.bird {
  position: absolute;
  width: 7px;
  height: 7px;
  transform: rotate(45deg);
  animation: moving 16s linear infinite;
}

.bird.-type_2 {
  animation-delay: 1s;
}
.bird.-type_2:before,
.bird.-type_2:after {
  animation-delay: -2s;
}

.bird.-type_3 {
  animation-delay: 3s;
}

@keyframes moving {
  0% {
    top: 47vh;
    left: -2vw;
  }
  25% {
    top: 51vh;
    left: 23vw
  }
  100% {
    top: 47vh;
    left: 101vw;
  }
}

.bird:before, .bird:after {
  content: "";
  position: absolute;
  bottom: 0;
  right: 0;
  background-color: black;
  transform: rotate(-30deg);
  transform-origin: right bottom;
}

.bird:before {
  width: 100%;
  height: 1px;
  animation: leftWing 8s linear infinite;
}
.bird:after {
  width: 1px;
  height: 100%;
  animation: rightWing 8s linear infinite;
}

@keyframes leftWing {
  0%   { transform: rotate(-30deg); }
  2%   { transform: rotate(-110deg); }
  4%   { transform: rotate(-30deg); }
  6%   { transform: rotate(-110deg); }
  8%   { transform: rotate(-30deg); }
  10%  { transform: rotate(-110deg); }
  12%  { transform: rotate(-30deg); }
  30%  { transform: rotate(-30deg); }
  42%  { transform: rotate(-35deg); }
  72%  { transform: rotate(-35deg); }
  74%  { transform: rotate(10deg); }
  76%  { transform: rotate(-30deg); }
  78%  { transform: rotate(-110deg); }
  80%  { transform: rotate(-30deg); }
  82%  { transform: rotate(-110deg); }
  84%  { transform: rotate(-30deg); }
  86%  { transform: rotate(-110deg); }
  88%  { transform: rotate(-30deg); }
  90%  { transform: rotate(-110deg); }
  92%  { transform: rotate(-30deg); }
  94%  { transform: rotate(-110deg); }
  96%  { transform: rotate(-30deg); }
  98%  { transform: rotate(-110deg); }
  100% { transform: rotate(-30deg); }
}

@keyframes rightWing {
  0%   { transform: rotate(30deg); }
  2%   { transform: rotate(110deg); }
  4%   { transform: rotate(30deg); }
  6%   { transform: rotate(110deg); }
  8%   { transform: rotate(30deg); }
  10%  { transform: rotate(110deg); }
  12%  { transform: rotate(30deg); }
  30%  { transform: rotate(30deg); }
  42%  { transform: rotate(35deg); }
  72%  { transform: rotate(35deg); }
  74%  { transform: rotate(0deg); }
  76%  { transform: rotate(30deg); }
  78%  { transform: rotate(110deg); }
  80%  { transform: rotate(30deg); }
  82%  { transform: rotate(110deg); }
  84%  { transform: rotate(30deg); }
  86%  { transform: rotate(110deg); }
  88%  { transform: rotate(30deg); }
  90%  { transform: rotate(110deg); }
  92%  { transform: rotate(30deg); }
  94%  { transform: rotate(110deg); }
  96%  { transform: rotate(30deg); }
  98%  { transform: rotate(110deg); }
  100% { transform: rotate(30deg); }
}

/****** Base style. ******/
body {
  overflow: hidden;
  height: 100vh;
  margin: 0;
}