ヘッダーメニューなどでよく見るドロップダウンメニューを実装！ソースコードあり！

<header class="header">
	<div class="inner">
		<h1 class="site-title">
			<!-- サイト名やサイトのロゴ -->
		</h1>
		<nav class="header-menu">
			<ul class="header-menu__list">
				<li class="header-menu__item pc">
					<a href="#">
						<span class="ja">メニュー1</span>
						<span class="en">Memu01</span>
					</a>
				</li>
				<li class="header-menu__item has-child">
					<span class="ja">メニュー2</span>
					<span class="en">Menu02</span>
					<ul class="header-menu__list02">
						<li class="header-menu__item02">
							<a href="#">メニュー2-1</a>
						</li>
						<li class="header-menu__item02">
							<a href="#">メニュー2-2</a>
						</li>
						<li class="header-menu__item02">
							<a href="#">メニュー2-3</a>
						</li>
						<li class="header-menu__item02">
							<a href="#">メニュー2-4</a>
						</li>
					</ul>
				</li>
				<li class="header-menu__item pc">
					<a href="#">
						<span class="ja">メニュー3</span>
						<span class="en">Memu03</span>
					</a>
				</li>
			</ul>
		</nav>
	</div>
</header>

.header {
    display: block;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 70px;
    background-color: #fff;
    transition: all 0.3s;
    z-index: 9999;
}
header .inner {
    display: flex;
    position: relative;
    height: 100%;
    padding: 0;
    align-items: center;
    justify-content: center;
    max-width: 1140px;
    margin: 0 auto;
}
.site-title a {
    white-space: nowrap;
    display: block;
    font-size: 20px;
    line-height: 70px;
}
.header-menu {
    width: 100%;
}
.header-menu__list {
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    background-color: #fff;
}
.header-menu__item {
    position: relative;
    text-align: center;
    font-size: 14px;
    font-weight: 700;
    border-left: 1px solid #ddd;
}
.header-menu__item > a {
    position: relative;
    padding: 0 20px;
}
.header-menu__item .en {
    font-size: 12px;
    color: #bbb;
    line-height: 1;
    font-weight: 400;
}
.header-menu__item > a,
.header-menu__item > a > span,
.header-menu__item > span {
    display: block;
}
.header-menu__item:last-child {
    border-right: 1px solid #ddd;
}
.header-menu__list02 {
    display: none;
}
.has-child:hover .header-menu__list02 {
    display: block;
    width: 100%;
    position: absolute;
    font-weight: 400;
    top: 40px;
    left: 0;
    padding: 8px 0;
    background-color: #fff;
    z-index: 1000;
    cursor: pointer;
    border-radius: 5px;
}
.header-menu__list02 a {
    display: block;
    padding: 5px 0;
}
.has-child {
    position: relative;
    text-align: center;
    cursor: pointer;
    padding-left: 20px;
    padding-right: 30px;
}
.has-child::after {
    content: "";
    display: inline-block;
    position: absolute;
    width: 7px;
    height: 7px;
    border-top: 2px solid #2c2c2c;
    border-right: 2px solid #2c2c2c;
    transition: all 0.3s;
    top: 12px;
    right: 10px;
    transform: rotate(135deg) translateY(-50%);
}

@media screen and (min-width: 768px) {
    .site-title a {
        padding-left: 20px;
    }
}