<div id="description">
  <h2>Приклад</h2>
  <p>Елемент з обчисленою шириною за допомогою функції hypot()</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: hypot(3em, 4em);
  height: 100px;
  background: blue;
}

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