<div id="description">
  <h2>Приклад 1</h2>
  <p>Елемент, що змінюється за допомогою анімації</p>
</div>

<div id="result">
  <div class="box"></div>
</div>

#description {
  font-style: italic;
  text-align: left;
  line-height: 1.5;
  margin-bottom: 50px;
  padding: 12px 16px;
  background-color: #f7f7f7;
  border: 1px solid #ccc;
}

#result {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 200px;
}

.box {
  width: 200px;
  height: 200px;
  background: blue;
  animation-name: myAnimation;
  animation-duration: calc(cos(0.25turn) * 1s);
}

@keyframes myAnimation {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}

External CSS

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External JavaScript

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