ハンバーガーメニュー：ボーダー（カスケード）｜Hamburger Menu: Border Cascade

<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="#">Menu 1</a>
        <a href="#">Menu 2</a>
        <a href="#">Menu 3</a>
    </nav>
</div>

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

.hamburger-menu {
    width: 32px;
    height: 24px;
    position: absolute;
    top: 20px;
    right: 20px;
    cursor: pointer;
    user-select: none;
    border: 2px solid #333;
    border-radius: 6px;
    padding: 6px;
    transition: all 0.3s;
}

.hamburger-menu:hover {
    border-color: #666;
    background: #f5f5f5;
}

.line {
    background-color: #333;
    height: 2px;
    width: calc(100% - 12px);
    position: absolute;
    transition: all 0.3s ease;
    left: 6px;
}

.line:nth-of-type(1) {
    top: 20%;
}

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

.line:nth-of-type(3) {
    bottom: 20%;
}

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

.hamburger-menu.active > .line:nth-of-type(2) {
    opacity: 0;
}

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

.nav-menu {
    display: none;
    flex-direction: column;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translateX(-50%) translateY(-50%);
    align-items: flex-start;
    justify-content: flex-start;
    padding: 0;
    width: 33%;
    min-height: 120px;
    max-height: 80%;
    background: white;
    border: 3px solid #333;
    border-radius: 10px;
    opacity: 0;
    overflow: hidden;
}

.nav-menu.active {
    display: flex;
    animation: slideInFromTop 0.4s forwards;
}

@keyframes slideInFromTop {
    0% {
        top: -100px;
        opacity: 0;
    }
    100% {
        top: 50%;
        opacity: 1;
    }
}

.nav-menu a {
    text-decoration: none;
    color: #333;
    padding: 15px 20px;
    margin: 0;
    width: 100%;
    text-align: center;
    border-bottom: 1px solid #ddd;
    transition: all 0.3s;
    opacity: 0;
    transform: translateY(-20px);
    pointer-events: none;
    position: relative;
    box-sizing: border-box;
}

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

.nav-menu a:hover {
    background: #f8f8f8;
    color: #333;
    padding-left: 25px;
}

document.addEventListener('DOMContentLoaded', function() {
    const hamburgerMenu = document.querySelector('.hamburger-menu');
    const navMenu = document.querySelector('.nav-menu');
    
    hamburgerMenu.addEventListener('click', () => {
        hamburgerMenu.classList.toggle('active');
        navMenu.classList.toggle('active');
        
        if (navMenu.classList.contains('active')) {
            const menuItems = navMenu.querySelectorAll('a');
            menuItems.forEach((item, index) => {
                setTimeout(() => {
                    item.classList.add('show');
                }, 250 + (index * 150));
            });
        } else {
            const menuItems = navMenu.querySelectorAll('a');
            menuItems.forEach(item => {
                item.classList.remove('show');
            });
        }
    });
});