JSFiddle - React, Tailwind, and code Playground

by VKorneva

HTML

<script src="//code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<link rel="stylesheet" href="//stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">
<script src="//cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.0/umd/popper.min.js"></script>
<script src="//stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css">
<div class="col-10 mt-5">
<label for="">Phone Number</label><br>
  <div class="form-group input-group">
    <div class="input-group-prepend">
      <select class="form-control input-group-text bg-transparent">
        <option>Code</option>
        <option>1234</option>
        <option>2234</option>
        <option>3234</option>
      </select>
    </div>
    <input class="form-control" placeholder="1234567" pattern="[0-9]">
  </div>
</div>

CSS

.form-control:focus,
.input-group:focus { 
outline: none; 
box-shadow:none;
}