loading.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  background-color: #f9fbff;
}
#logo {
  height: 100px;
  width: 100px;
  position: relative;
}
#logo > div {
  position: absolute;
}
.loading {
  margin-top: 50px;
}
#a,
#b {
  width: 20px;
  height: 20px;
}
#a {
  background: red;
  top: 0;
  left: 0;
  animation: a 2s infinite;
}
#b {
  background: blue;
  right: 0;
  bottom: 0;
  animation: b 2s infinite;
}
#c,
#d,
#e {
  background: black;
  height: 2px;
  width: 140px;
  left: -20px;
}
#c {
  top: 0px;
}
#d {
  top: 20px;
  animation: d 2s infinite;
}
#e {
  bottom: 0px;
}
#f,
#g,
#h {
  background: black;
  width: 2px;
  height: 140px;
  top: -20px;
}
#f {
  left: 0;
}
#g {
  left: 20px;
  animation: g 2s infinite;
}
#h {
  right: 0;
}
@keyframes d {
  0% {
    top: 20px;
  }
  25% {
    top: 20px;
  }
  50% {
    top: 80px;
  }
  75% {
    top: 80px;
  }
  100% {
    top: 20px;
  }
}
@keyframes g {
  0% {
    left: 20px;
  }
  25% {
    left: 80px;
  }
  50% {
    left: 80px;
  }
  75% {
    left: 20px;
  }
  100% {
    left: 20px;
  }
}
@keyframes a {
  0% {
    width: 20px;
    height: 20px;
  }
  25% {
    width: 80px;
    height: 20px;
  }
  50% {
    width: 80px;
    height: 80px;
  }
  75% {
    width: 20px;
    height: 80px;
  }
  100% {
    width: 20px;
    height: 20px;
  }
}
@keyframes b {
  0% {
    width: 80px;
    height: 80px;
  }
  25% {
    width: 20px;
    height: 80px;
  }
  50% {
    width: 20px;
    height: 20px;
  }
  75% {
    width: 80px;
    height: 20px;
  }
  100% {
    width: 80px;
    height: 80px;
  }
}