JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Imasen Test</title>
    <link rel="stylesheet" href="css/style.css">
</head>

<body>
    <!-- header -->
    <section class="header">
        <nav>
            <a href=""><img src="../test/img/logo.svg" width="213" height="42"></a>
            <div class="nav-links">
                <ul>
                    <li><a href="">หน้าหลัก</a></li>
                    <li><a href="">เกี่ยวกับเรา</a>
                        <div class="dropdown-menu">
                        <ul>
                            <li><a href="">Page 1</a></li>
                            <li><a href="">Page 2</a></li>
                            <li><a href="">Page 3</a></li>
                        </ul>
                    </div>
                    </li>
                    <li><a href="">ผลิตภัณฑ์</a></li>
                    <li><a href="">กิจกรรมเพื่อสังคม</a></li>
                    <li><a href="">นักลงทุน</a></li>
                    <li><a href="">ติดต่อเรา</a></li>
                </ul>
            </div>
        </nav>
    </section>
</body>

</html>

CSS

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

.header {
    min-height: 100vh;
    width: 100%;
    background-image: linear-gradient(rgba(4, 9, 30, 0.5), rgba(4, 9, 30, 0.5)), url("../img/heehehehehe.jpg");
    background-position: center;
    background-size: cover;
    position: relative;
}

nav {
    display: flex;
    padding: 2% 3%;
    justify-content: space-between;
    align-items: center;
    
}

.nav-links {
    flex: 1;
    text-align: center;
    font-size: 18px;
    font-weight: bold;
}

.nav-links ul li {
    list-style: none;
    display: inline-block;
    position: relative;
    padding-bottom: 0.5rem;

}

.nav-links ul li a {
    color: #fff;
    text-decoration: none;
}

.nav-links ul li::after {
    content: '';
    position: absolute;
    width: 0;
    height: 2px;
    background: #fff;
    right: 0;
    bottom: 0;
    transition: width 0.25s ease-out;    
}

.nav-links ul li:hover::after {
    width: 100%;
    left: 0;
    right: auto;
}


.dropdown-menu {
    display: none;
}

.nav-links ul li:hover .dropdown-menu {
    display: block;
    position: absolute;
    left: 0;
    top: 100%;
    background: linear-gradient(rgba(1, 1, 1, 0.4), rgba(1, 1, 1, 0.4));
}

.dropdown-menu ul {
    display: block;
    margin: 10px;
}

.dropdown-menu ul li {
    width: 150px;
    padding: 10px;
    text-align: left;
}