【2025年版】CSSのみでドロップダウンメニューを作る方法｜JavaScript不要で簡単実装

.navbar {
background-color: #2c3e50;
padding: 0;
}

.menu {
list-style: none;
margin: 0;
padding: 0;
display: flex;
}

.menu-item {
position: relative;
}

.menu-link {
display: block;
color: white;
text-decoration: none;
padding: 16px 20px;
transition: background-color 0.3s ease;
}

.menu-link:hover {
background-color: #34495e;
}

.dropdown {
position: absolute;
top: 100%;
left: 0;
background-color: #34495e;
list-style: none;
margin: 0;
padding: 0;
min-width: 200px;
opacity: 0;
visibility: hidden;
transform: translateY(-10px);
transition: all 0.3s ease;
box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.has-dropdown:hover .dropdown {
opacity: 1;
visibility: visible;
transform: translateY(0);
}

.dropdown-link {
display: block;
color: white;
text-decoration: none;
padding: 12px 20px;
border-bottom: 1px solid #2c3e50;
transition: background-color 0.3s ease;
}

.dropdown-link:hover {
background-color: #2c3e50;
}

.dropdown li:last-child .dropdown-link {
border-bottom: none;
}

.advanced-navbar {
background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
padding: 0;
box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
}

.advanced-menu {
list-style: none;
margin: 0;
padding: 0;
display: flex;
}

.advanced-item {
position: relative;
}

.advanced-link {
display: flex;
align-items: center;
color: white;
text-decoration: none;
padding: 18px 24px;
transition: all 0.3s ease;
font-weight: 500;
}

.advanced-link:hover {
background-color: rgba(255, 255, 255, 0.1);
transform: translateY(-2px);
}

.arrow {
margin-left: 8px;
font-size: 12px;
transition: transform 0.3s ease;
}

.has-advanced-dropdown:hover .arrow {
transform: rotate(180deg);
}

.advanced-dropdown {
position: absolute;
top: 100%;
left: 0;
background-color: white;
list-style: none;
margin: 0;
padding: 8px 0;
min-width: 220px;
opacity: 0;
visibility: hidden;
transform: translateY(-20px) scale(0.95);
transition: all 0.4s cubic-bezier(0.68, -0.55, 0.265, 1.55);
box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
border-radius: 8px;
z-index: 1000;
}

.has-advanced-dropdown:hover .advanced-dropdown {
opacity: 1;
visibility: visible;
transform: translateY(0) scale(1);
}

.advanced-dropdown-link {
display: block;
color: #333;
text-decoration: none;
padding: 12px 24px;
transition: all 0.3s ease;
border-left: 3px solid transparent;
}

.advanced-dropdown-link:hover {
background-color: #f8f9fa;
border-left-color: #667eea;
transform: translateX(5px);
}