ハンバーガーメニュー：シンプル（カスケード・サイド）｜Hamburger Menu: Simple Cascade Side

<div class="container">
    <div class="hamburger-menu">
        <div class="line"></div>
        <div class="line"></div>
        <div class="line"></div>
    </div>
    <nav class="nav-menu">
        <a href="#">メニュー1</a>
        <a href="#">メニュー2</a>
        <a href="#">メニュー3</a>
    </nav>
</div>

.container {
    position: relative;
    width: 100%;
    height: 300px;
    border: 2px solid #333;
    border-radius: 8px;
    overflow: hidden;
}

.hamburger-menu {
    width: 30px;
    height: 22px;
    position: absolute;
    top: 20px;
    right: 20px;
    cursor: pointer;
    user-select: none;
}

.line {
    background-color: black;
    height: 4px;
    width: 100%;
    position: absolute;
    transition: all 0.3s;
}

.line:nth-of-type(1) {
    top: 0;
}

.line:nth-of-type(2) {
    top: 50%;
    transform: translateY(-50%);
}

.line:nth-of-type(3) {
    bottom: 0;
}

.hamburger-menu.active > .line:nth-of-type(1) {
    top: 50%;
    transform: translateY(-50%) rotate(45deg);
}

.hamburger-menu.active > .line:nth-of-type(2) {
    display: none;
}

.hamburger-menu.active > .line:nth-of-type(3) {
    top: 50%;
    transform: translateY(-50%) rotate(-45deg);
}

.nav-menu {
    display: none;
    flex-direction: column;
    position: absolute;
    top: 0;
    left: 0;
    align-items: flex-start;
    justify-content: flex-start;
    padding: 20px 8px 8px 8px;
    width: 33%;
    height: 100%;
    background-color: #f5f5f5;
    opacity: 0;
}

.nav-menu.active {
    display: flex;
    animation: slideInFromLeft 0.3s forwards;
}

@keyframes slideInFromLeft {
    0% {
        left: -100%;
        opacity: 0;
    }
    100% {
        left: 0;
        opacity: 1;
    }
}

.nav-menu a {
    text-decoration: none;
    color: black;
    padding: 5px;
    margin: 5px;
    opacity: 0;
    transform: translateX(-20px);
    transition: all 0.3s ease;
    pointer-events: none;
}

.nav-menu a.show {
    opacity: 1;
    transform: translateX(0);
    pointer-events: auto;
}

document.querySelector('.hamburger-menu').addEventListener('click', function() {
    this.classList.toggle('active');
    const navMenu = this.nextElementSibling;
    navMenu.classList.toggle('active');
    
    if (navMenu.classList.contains('active')) {
        // メニューを順番に表示
        const menuItems = navMenu.querySelectorAll('a');
        menuItems.forEach((item, index) => {
            setTimeout(() => {
                item.classList.add('show');
            }, 250 + (index * 150)); // メニューウィンドウのアニメーション後から開始
        });
    } else {
        // メニューを非表示
        const menuItems = navMenu.querySelectorAll('a');
        menuItems.forEach(item => {
            item.classList.remove('show');
        });
    }
});