タブメニュー：スライドボタン｜Tab Menu: Slide Button

<div class="container">
    <h1>Tab Menu - Slide Button</h1>
    
    <div class="tab-container">
        <ul>
            <div class="slide-indicator"></div>
            <li class="selected" data-id="tab-1">Tab 1</li>
            <li data-id="tab-2">Tab 2</li>
            <li data-id="tab-3">Tab 3</li>
        </ul>
        <div class="tab-content selected" id="tab-1">
            Good morning. This is the content of Tab 1.
        </div>
        <div class="tab-content" id="tab-2">
            Hello. This is the content of Tab 2.
        </div>
        <div class="tab-content" id="tab-3">
            Good evening. This is the content of Tab 3.
        </div>
    </div>
</div>

.container {
    margin: 0 auto;
    border-radius: 12px;
    padding: 20px;
    max-width: 600px;
    width: 100%;
}

.tab-container {
    position: relative;
}

.tab-container ul {
    margin: 0;
    padding: 0;
    list-style: none;
    display: flex;
    background: #eeeeee;
    border-radius: 48px;
    padding: 6px;
    position: relative;
}

.slide-indicator {
    position: absolute;
    top: 6px;
    left: 6px;
    width: calc(33.333% - 4px);
    height: calc(100% - 12px);
    background: linear-gradient(135deg, #4a4a4a 0%, #2c2c2c 100%);
    border-radius: 48px;
    transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    z-index: 1;
}

.tab-container ul li {
    flex: 1;
    padding: 14px 18px;
    text-align: center;
    cursor: pointer;
    transition: all 0.3s ease;
    position: relative;
    z-index: 2;
    font-weight: 500;
    font-size: 14px;
    color: #333333;
    border-radius: 8px;
    margin: 0 2px;
    background: transparent;
}

.tab-container ul li.selected {
    color: #ffffff;
    font-weight: 600;
    text-shadow: 0 1px 2px rgba(0, 0, 0, 0.3);
}

.tab-container ul li:not(.selected):hover {
    color: #aaaaaa;
    background: rgba(255, 255, 255, 0.1);
    transform: translateY(-1px);
}

.tab-content {
    display: none;
    padding: 24px;
    min-height: 150px;
    background: #fefefe;
    border: 1px solid #e0e0e0;
    border-radius: 8px;
    margin-top: 16px;
}

.tab-content.selected {
    display: block;
    animation: slideContentIn 0.3s ease-out;
}

@keyframes slideContentIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

h1 {
    text-align: center;
    color: #333;
    margin-bottom: 30px;
    font-size: 24px;
    font-weight: 600;
}

const tabContainer = document.querySelector('.tab-container');
const tabMenuItems = tabContainer.querySelectorAll('ul li');
const tabContents = tabContainer.querySelectorAll('.tab-content');
const slideIndicator = tabContainer.querySelector('.slide-indicator');

tabMenuItems.forEach((tabMenuItem, index) => {
    tabMenuItem.addEventListener('click', () => {
        // 現在のコンテナ内の全てのタブからselectedクラスを外す
        tabMenuItems.forEach(item => {
            item.classList.remove('selected');
        });
        
        // クリックされたタブのみselectedクラスを付ける
        tabMenuItem.classList.add('selected');
        
        // 現在のコンテナ内の全てのタブのコンテンツからselectedクラスを外す
        tabContents.forEach(tabContent => {
            tabContent.classList.remove('selected');
        });

        // クリックされたタブのカスタムデータ属性と同じIDを持つコンテンツに、selectedクラスを付ける
        document.getElementById(tabMenuItem.dataset.id).classList.add('selected');

        // スライドインジケーターの位置を更新
        slideIndicator.style.transform = `translateX(${index * 100}%)`;
    });
});