<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<div class="container" style="margin-top: 1em;">
<form>
<div class="card person-card">
<div class="card-body">
<img id="img_sex" class="person-img"
src="https://visualpharm.com/assets/217/Life%20Cycle-595b40b75ba036ed117d9ef0.svg">
<h2 id="who_message" class="card-title">Who are you ?</h2>
<div class="row">
<div class="form-group col-md-2">
<select id="input_sex" class="form-control">
<option value="Mr.">Mr.</option>
<option value="Ms.">Ms.</option>
</select>
</div>
<div class="form-group col-md-5">
<input id="first_name" type="text" class="form-control" placeholder="First name">
<div id="first_name_feedback" class="invalid-feedback">
</div>
</div>
<div class="form-group col-md-5">
<input id="last_name" type="text" class="form-control" placeholder="Last name">
<div id="last_name_feedback" class="invalid-feedback">