JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
<div class="col-sm-6">
  <div class="input-group">
     <div class="iban">
        <input type="text" name="iban" class="form-control text-uppercase">
     </div>

     <div class="input-group-addon">
        <span class="glyphicon"></span>
     </div>
  </div>
</div>

CSS

.iban:before {
  content: 'CH';
  color: #999;
  position:absolute;
  padding-left:7px;
  padding-top:7px;
  z-index:1000;
}

.iban > input {
  padding-left:29px;
}