스크롤

css

:root {
	overflow-y: overlay;
}

::-webkit-scrollbar-thumb {
	background-color: rgba(255, 0, 0, 0.2);
	border-radius: 10px;
	cursor: pointer;
}

::-webkit-scrollbar {
	width: 40px;
	height: 40px;
	background-color: rgba(0, 0, 0, .1);
}

밑줄

<!-- 테일윈드 -->
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/tailwindcss/2.2.19/tailwind.min.css">

<nav class="menu_1">
	<ul class="flex">
		<li><a href="#">내용 1</a></li>
		<li><a href="#">내용 22</a></li>
		<li><a href="#">내용 333</a></li>
		<li><a href="#">내용 4444</a></li>
		<li><a href="#">내용 55555</a></li>
	</ul>
</nav>

<nav class="menu_2">
	<ul class="flex">
		<li><a href="#">내용 1</a></li>
		<li><a href="#">내용 22</a></li>
		<li><a href="#">내용 333</a></li>
		<li><a href="#">내용 4444</a></li>
		<li><a href="#">내용 55555</a></li>
	</ul>
</nav>

<nav class="menu_3">
	<ul class="flex">
		<li><a href="#"><span>내용 1</span></a></li>
		<li><a href="#"><span>내용 22</span></a></li>
		<li><a href="#"><span>내용 333</span></a></li>
		<li><a href="#"><span>내용 4444</span></a></li>
		<li><a href="#"><span>내용 55555</span></a></li>
	</ul>
</nav>

body {
	min-height: 100vh;
	display: flex;
	align-items: center;
	justify-content: center;
	flex-direction: column;
	gap: 20px;
}

/* 방법1 */
.menu_1 > ul > li > a {
	display: block;
	padding: 20px;
	position: relative;
}

.menu_1 > ul > li > a::after {
	content: "";
	position: absolute;
	bottom: 0;
	left: 20px;
	right: 20px;
	height: 10px;
	background-color: red;
}

/* 방법2 */
.menu_2 > ul > li > a {
	display: block;
	padding: 20px;
	position: relative;
}

.menu_2 > ul > li > a::after {
	content: "";
	position: absolute;
	bottom: 0;
	left: 20px;
	width: calc(100% - 40px);
	height: 10px;
	background-color: red;
}

/* 방법3 */
.menu_3 > ul > li > a {
	display: flex;
	padding: 0 20px;
}

.menu_3 > ul > li > a > span {
	display: inline-block;
	position: relative;
	padding: 20px 0;
}

.menu_3 > ul > li > a > span::after {
	content: "";
	position: absolute;
	bottom: 0;
	left: 0;
	width: 100%;
	height: 10px;
	background-color: red;
}