JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://getbootstrap.com/dist/css/bootstrap.css">
<script src="http://getbootstrap.com/dist/js/bootstrap.js"></script>
 <div class="form-group has-feedback size-input-wrapper">
    <label class="control-label" for="inputValidation">Enter size:</label>
    <input type="number" class="form-control" id="inputValidation" placeholder="size"/>
    <span class="form-control-feedback">px</span>
 </div>

CSS

.size-input-wrapper {
    max-width: 140px;
    margin: auto;
}