JSFiddle - React, Tailwind, and code Playground

HTML

<div class="fixed-top">
    <span class="trigger">hover me</span>
    <div class="menu"></div>
</div>

CSS

body {
    margin: 0;
}
.fixed-top {
    height: 50px;
    width: 100%;
    padding: 0;
    top: 0;
    position: fixed;
}
.fixed-top:before {
    background: #3b5999;
    content:'';
    position: absolute;
    top: 0; right: 0; bottom: 0; left: 0;
    z-index: 1;
}
.trigger {
    color: white;
    font-size: 33px;
    margin-left: 50%;
    position: relative;
    z-index: 2;
}
.trigger:hover + .menu {
    margin-top: 0;
}
.menu {
    z-index: 0;
    height: 300px;
    background-color: #1c7754;
    width: 400px;
    margin: auto;
    margin-top: -400px;
    transition: all 0.75s ease-out;
}