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HTML

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Adding Classes

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About the <head>

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CSS

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CSS Base

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JavaScript

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JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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HTML 

              
                <section class="qna" itemscope itemtype="https://schema.org/FAQPage">
  <h2>Вопросы и ответы</h2>
  <div class="qna__items">

    <details class="qna__item" itemscope itemprop="mainEntity" itemtype="https://schema.org/Question">
      <summary class="qna__question" itemprop="name">Что такое HTML?</summary>
      <div class="qna__answer" itemscope itemprop="acceptedAnswer" itemtype="https://schema.org/Answer">
        <div class="qna__text" itemprop="text">
          <p>HTML расшифровывается как HyperText Markup Language (язык гипертекстовой разметки). Это язык разметки документов во Всемирной паутине (World Wide Web, WWW). HTML — это стандартизированный язык, позволяющий составлять форматированный текст. Браузер интерпретирует его и отображает на экране элементы веб-страниц.</p>
        </div>
      </div>
    </details>

    <details class="qna__item" itemscope itemprop="mainEntity" itemtype="https://schema.org/Question">
      <summary class="qna__question" itemprop="name">Зачем использовать списки в HTML?</summary>
      <div class="qna__answer" itemscope itemprop="acceptedAnswer" itemtype="https://schema.org/Answer">
        <div class="qna__text" itemprop="text">
          <p>Списки делают информацию более наглядной и удобной дляотображения элементов списка) тоже можно использовать различные теги. восприятия. Более того, внутри списков (точнее, для произвольного отображения элементов списка) тоже можно использовать различные теги.</p>
        </div>
      </div>
    </details>

    <details class="qna__item" itemscope itemprop="mainEntity" itemtype="https://schema.org/Question">
      <summary class="qna__question" itemprop="name">Для чего нужны таблицы стилей (CSS)?</summary>
      <div class="qna__answer" itemscope itemprop="acceptedAnswer" itemtype="https://schema.org/Answer">
        <div class="qna__text" itemprop="text">
          <p>Таблицы стилей позволяют задать чёткие правила, которые определяют внешний вид контента, тех или иных HTML-элементов и всей страницы в целом. Более того, одни и те же правила можно применять сразу к нескольким веб-страницам, что упрощает сохранение и, при необходимости, изменение единого стиля сайта.</p>
        </div>
      </div>
    </details>

  </div>
</section>
!

CSS 

              
                body {
  font-family: sans-serif;
  font-size: 16px;
}

p {
  margin: 0;
}

.qna {
  --animation-duration: 0.3s;
  --border-color: #ccc;
  width: clamp(300px, 50%, 800px);
  margin: 50px auto;

  &__item {
    margin: -1px 0 0;
    border: 1px solid var(--border-color);
    transition: var(--animation-duration);

    &:not(.js-details)[open],
    &.is-open {
      --border-color: #666;
      position: relative;
    }
  }

  &__question {
    position: relative;
    padding: 20px 50px 20px 20px;
    list-style: none; /* убираем стандартный маркер Firefox */
    cursor: pointer;

    &::after {
      content: '';
      position: absolute;
      top: calc(50% - 4px);
      right: 20px;
      width: 12px;
      height: 8px;
      background: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='none' viewBox='0 0 12 8'%3E%3Cpath stroke='%23999' stroke-width='2' d='M1 1l5 5 5-5'/%3E%3C/svg%3E");
      transition: var(--animation-duration);

      .qna__item:not(.js-details)[open] &,
      .qna__item.is-open & {
        transform: rotate(-180deg);
      }
    }

    &::-webkit-details-marker {
      display: none; /* убираем стандартный маркер Chrome */
    }
  }

  &__answer {
    .js-details & {
      max-height: 0;
      overflow: hidden;
      animation: slideUp var(--animation-duration);
    }

    .js-details.is-open & {
      max-height: none;
      animation: slideDown var(--animation-duration);
    }

    .js-details.is-open.is-animating & {
      max-height: var(--details-height);
    }
  }

  &__text {
    padding: 0 20px 20px;
  }
}

@keyframes slideUp {
  0% {
    max-height: var(--details-height);
    opacity: 1;
  }

  100% {
    max-height: 0;
    opacity: 0;
  }
}

@keyframes slideDown {
  0% {
    max-height: 0;
    opacity: 0;
  }

  100% {
    max-height: var(--details-height);
    opacity: 1;
  }
}
!

JS 

              
                document.querySelectorAll('.qna__item').forEach(item => {
  const minimizeSiblings = true
  const question = item.querySelector('.qna__question')
  const answer = item.querySelector('.qna__answer')
  const cssDuration = getComputedStyle(answer).getPropertyValue('--animation-duration')
  const animationDuration = Number.parseInt(Number.parseFloat(cssDuration) * (/\ds$/.test(cssDuration) ? 1000 : 1))
  const setHeight = () => answer.style.setProperty('--details-height', `${answer.scrollHeight}px`)

  item.classList.add('js-details')

  const onClick = event => {
    setHeight()

    let isAnimating = true
    item.classList.toggle('is-open')
    item.classList.add('is-animating')

    setTimeout(() => {
      item.classList.remove('is-animating')
    }, animationDuration)

    if (item.open) {
      event.preventDefault()
      if (isAnimating) return
      setTimeout(() => {
        item.open = false
        isAnimating = false
      }, animationDuration)
    }

    if (!minimizeSiblings) return

    const siblings = [...item.parentNode.children]
      .filter(el => el.classList.contains('js-details'))
      .filter(el => el !== event.target.parentNode)

    for (const el of siblings) {
      el.classList.remove('is-open')
      setTimeout(() => {
        el.open = false
      }, animationDuration)
    }
  }

  question.addEventListener('click', onClick)
})
!
999px

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