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CSS

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HTML 

              
                <div class="c-switching">
   <div class="c-switchingTabs">
     <button class="js-switchingTab is-current c-switchingTabs__tab" type="button" data-switch-tab="type01"><span>その1<small>（初期値には<code>.is-current</code>を付与）</small></span></button>
     <button class="js-switchingTab c-switchingTabs__tab" type="button" data-switch-tab="type02">その2</button>
     <button class="js-switchingTab c-switchingTabs__tab" type="button" data-switch-tab="type03">その3</button>
   </div>
  <div class="c-switchingContainer">
    <div class="js-switchingContents is-open c-switchingContainer__contents" data-switch-contents="type01">
      <p>その1のコンテンツ内容が表示されます。<br>
        （初期値にしたいコンテンツには<code>.is-open</code>を付与する）</p>
      <button class="js-switchingTab c-btn" type="button" data-switch-tab="type02">その2 を表示する</button>
    </div>
    <div class="js-switchingContents c-switchingContainer__contents" data-switch-contents="type02">
      <p>その2のコンテンツ内容が表示されます。</p>
      <button class="js-switchingTab c-btn" type="button" data-switch-tab="type03">その3 を表示する</button>
    </div>
    <div class="js-switchingContents c-switchingContainer__contents" data-switch-contents="type03">
      <p>その3のコンテンツ内容が表示されます。<br>ボタンがどこにあっても大丈夫！</p>
      <button class="js-switchingTab c-btn is-current" type="button" data-switch-tab="type01">その1 を表示する</button>
    </div>
  </div>
</div>
<button class="js-switchingTab c-btn is-current" type="button" data-switch-tab="type01">その1 を表示する</button>
<button class="js-switchingTab c-btn" type="button" data-switch-tab="type02">その2 を表示する</button>
<button class="js-switchingTab c-btn" type="button" data-switch-tab="type03">その3 を表示する</button>
!

CSS 

              
                * {
  font-size: 16px;
  line-height: 1.8;
  color: #333;
}
small {
  font-size: max(0.7em, 12px);
}

.c-btn {
  display: flex;
  justify-content: center;
  align-items: center;
  min-width: 200px;
  padding: 0.8em 1em;
  border: 1px solid #333;
  border-radius: 2em;
  background: #fff;
  color: #333;
  cursor: pointer;
  transition: .3s;
  &:hover, &.is-current {
    background: #333;
    color: #fff;
  }
  &:not(:first-child) {
    margin-top: 2em;
  }
}

.c-switchingTabs {
  display: flex;
  gap: 20px;
  margin-bottom: -1px;
  &__tab {
    display: flex;
    justify-content: center;
    align-items: center;
    min-width: 200px;
    padding: 0.5em 1em;
    border: 1px solid #333;
    border-bottom: none;
    border-radius: 20px 20px 0 0;
    background: lightgray;
    font-size: 20px;
    line-height: 1.4;
    cursor: pointer;
    transition: .3s;
    &:hover, &.is-current {
      background: lightblue;
    }
  }
}
.c-switchingContainer {
  width: min(100%, 1000px);
  padding: 5em 1em 6em;
  border: 1px solid #333;
  background: lightblue;
  &__contents {
    width: 100%;
  }
}

.js-switchingContents {
  height: 0;
  opacity: 0;
  overflow: hidden;
  transition: .3s;
  &.is-open {
    height: auto;
    opacity: 1;
  }
}
!

JS 

              
                // HTML要素を取得
const switchingTabs = document.querySelectorAll('.js-switchingTab');
const switchingContents = document.querySelectorAll('.js-switchingContents');

// タブボタンにクリックイベントを追加
switchingTabs.forEach(tabButton => {
  tabButton.addEventListener('click', () => {
    // クリックされたタブボタンのdata-switch-tab属性の値を取得
    const targetTab = tabButton.getAttribute('data-switch-tab');
    
    // 対応するコンテンツ要素を探す
    const targetContent = document.querySelector(`[data-switch-contents="${targetTab}"]`);
    
    // すべてのコンテンツ要素から.is-openクラスを削除
    switchingContents.forEach(switchingContent => {
      switchingContent.classList.remove('is-open');
    });
    
    // 対応するコンテンツ要素に.is-openクラスを追加
    targetContent.classList.add('is-open');

    // すべてのタブボタンから.is-currentクラスを削除
    switchingTabs.forEach(tabButton => {
      tabButton.classList.remove('is-current');
    });

    // クリックされたタブボタンに.is-currentクラスを追加
    tabButton.classList.add('is-current');

    // 同じdata-switch-tab属性の値を持つ他のタブボタンにも.is-currentクラスを追加
    switchingTabs.forEach(otherTabButton => {
      if (otherTabButton !== tabButton && otherTabButton.getAttribute('data-switch-tab') === targetTab) {
        otherTabButton.classList.add('is-current');
      }
    });
  });
});
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999px

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