JSFiddle - React, Tailwind, and code Playground

HTML

<div class="loader">
    <div class="bar"></div>
</div>

CSS

@keyframes loader-animation {
    0% {
        width: 0%;
    }
    49% {
        width: 100%;
        left: 0%
    }
   
}
.loader {
    height: 5px;
    width: 100%;
}
.loader .bar {
    position: relative;
    height: 5px;
    border-top: 1px solid black;
    animation-name: loader-animation;
    animation-duration: 3s;
}