コピペでCSS　よくあるプルダウンメニューボタンPC版

HTML

<div class="naviBox">
	<div class="navi">
		<ul>
			<li>
				<a href="#">page1</a>
				<ul>
					<li><a href="#">sub page1</a></li>
					<li><a href="#">sub page2</a></li>
				</ul>
			</li>
			<li>
				<a href="#">page2</a>
				<ul>
					<li><a href="#">sub page3</a></li>
					<li>
						<a href="#">sub page4</a>
						<ul>
							<li><a href="#">child page</a></li>
							<li><a href="#">child page</a></li>
				
						</ul>
					</li>
					<li>
						<a href="#">sub page5</a>
						<ul>
							<li><a href="#">child page</a></li>
							<li><a href="#">child page</a></li>
						
						</ul>
					</li>
				</ul>
			</li>
	</ul>
	</div>
</div>

CSS

.naviBox{
height:300px;
}
.navi ul {
	position: relative;
	margin: 0;
	padding: 0;
	list-style: none;
}
.navi ul::after {
	display: block;
	clear: both;
	content: '';
}
.navi ul li {
	position: relative;
	float: left;
	border: 2px solid #fff;
        background-color: #001c31;
        width: 200px;

}
.navi ul li:hover {
	background-color: rgba(0,113,198,.3);
}

.navi ul li:not(:first-child) {
	border-left: none;
}
.navi ul li a {
	display: inline-block;
	padding: 20px 50px;
	color: #fff;
	line-height: 1;
	text-align: center;
	text-decoration: none;
	white-space: nowrap;
}
.navi ul ul {
	position: absolute;
	top: 100%;
	left: -2px;
        visibility: hidden;
	opacity: 0;
	transition: .2s ease-in-out;
}
.navi ul ul li {
	float: none;
	margin: 0;
}
.navi ul ul li:not(:first-child) {
	border: 2px solid #fff;
	border-top: none;
}
.navi ul ul ul {
	position: absolute;
	top: -2px;
	left: 100%;
}
.navi ul ul {

}
.navi ul li:hover > ul {
	visibility: visible;
	opacity: 1;
}

結果

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