JSFiddle - React, Tailwind, and code Playground

HTML

<div id="menu">
    <div id="left_line"></div>
<ul>
    <li>Главная</li>
    <li>Пункт 1</li>
    <li>Пункт 2</li>
    <li>Пункт 3</li>
    <li>Пункт 4</li>
</ul>
</div>

CSS

#menu {
    position: relative;
	height:40px;
    text-align:center;
    margin-top:10px;
}

#menu li {
	display:inline-block;
	border:1px;
	border-color:#b8b8b8;
	border-style:solid;
	padding:10px;

	background: yellow;
     margin-left: -.36em;
}

#menu li a{
	font-size:16px;
	color:black;
	text-decoration:none;
}

#left_line {
    position: absolute;
  z-index: -100;
    top: 14px;
 	height:15px;
    width: 100%;
    background:#ccc;
 
}