JSFiddle - React, Tailwind, and code Playground

HTML

<div class="arrow up"></div>
<br>
<div class="arrow"></div>

CSS

body {
    padding: 20px;
}

.arrow {
   height: 5px;
   width: 5px;
   border: 4px solid blue;
}
.arrow.up {
   border-bottom-color: #000;
}
.arrow.down {
   border-top-color: #000;
}