JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
<form class="bs-example bs-example-form" data-example-id="simple-input-groups">
  <div class="input-group">
    <div class="input-group-addon" id="basic-addon1">@</div>
    <div class="form-control" placeholder="Username" aria-describedby="basic-addon1"> </div>
  </div>  
</form>

CSS

.input-group .form-control {
  width: 110%;
}