JSFiddle - React, Tailwind, and code Playground

by Palpatim

HTML

<div class="navback"></div>

CSS

.navback {
    position: absolute;
    width: 0;
    height: 17px;
    background-color: #FFF;
    border-top: 1px solid red;
    z-index: 999;
    transform: translate(-50%, -50%);
    top: 50%;
    left: 50%;
    -webkit-animation: expandline 5s linear;
}

@-webkit-keyframes expandline {
    0%   { width:   0%; }
    100% { width: 100%; }
}

.navback.onload {
    width:100%;
}