CSS is a box that has been climbing

HTML：

<div id="loader">
  <div id="box"></div>
  <div id="hill"></div>
</div>

CSS：

html, body {
    
  background-color: #404456;
}

#loader {
    
  position: absolute;
  top: 50%;
  left: 50%;
  margin-top: -2.7em;
  margin-left: -2.7em;
  width: 5.4em;
  height: 5.4em;
  background-color: #404456;
}

#hill {
    
  position: absolute;
  width: 7.1em;
  height: 7.1em;
  top: 1.7em;
  left: 1.7em;
  background-color: transparent;
  border-left: .25em solid whitesmoke;
  transform: rotate(45deg);
}

#hill:after {
    
  content: '';
  position: absolute;
  width: 7.1em;
  height: 7.1em;
  left: 0;
  background-color: #404456;
}

#box {
    
  position: absolute;
  left: 0;
  bottom: -.1em;
  width: 1em;
  height: 1em;
  background-color: transparent;
  border: .25em solid whitesmoke;
  border-radius: 15%;
  transform: translate(0, -1em) rotate(-45deg);
  animation: push 2.5s cubic-bezier(.79, 0, .47, .97) infinite;
}

@keyframes push {
    
  0% {
    
    transform: translate(0, -1em) rotate(-45deg);
  }
  5% {
    
    transform: translate(0, -1em) rotate(-50deg);
  }
  20% {
    
    transform: translate(1em, -2em) rotate(47deg);
  }
  25% {
    
    transform: translate(1em, -2em) rotate(45deg);
  }
  30% {
    
    transform: translate(1em, -2em) rotate(40deg);
  }
  45% {
    
    transform: translate(2em, -3em) rotate(137deg);
  }
  50% {
    
    transform: translate(2em, -3em) rotate(135deg);
  }
  55% {
    
    transform: translate(2em, -3em) rotate(130deg);
  }
  70% {
    
    transform: translate(3em, -4em) rotate(217deg);
  }
  75% {
    
    transform: translate(3em, -4em) rotate(220deg);
  }
  100% {
    
    transform: translate(0, -1em) rotate(-225deg);
  }
}