JSFiddle - React, Tailwind, and code Playground

HTML

<aside class="span4">

    <textarea cols="40" rows="20"></textarea>

</aside>

CSS

textarea {
			width: 100%;
			margin:0;
			padding:0;
    -webkit-box-sizing:border-box;
    -moz-box-sizing:border-box;
    box-sizing:border-box;

		}

		.span4 {
			width: 300px;
			
		}

		aside {
			overflow: auto;
		}