Two of my pages have a small gap under the footer - html

Question

All of my other pages do not have this gap, I am using Bootstrap but am a beginner. What do you think it could be? Is the whole page coded wrong because the contact form works fine, just when I am on a mobile device I can see a very thin white line under the footer.
<div class="section-md">
<div class="container container-normal">
<div class="row">
<div class="col-md-6 col-sm-6 col-md-offset-3 col-sm-offset-3">
<div class="panel panel-default">
<div class="panel-body">
<?php if (isset($_SESSION[ 'contact_success'])): ?>
<h2>Message Sent</h2>
<div class="alert alert-success">
Your information has been received. We will contact you within 1 business day.
</div>
Back to Homepage
<?php unset($_SESSION[ 'contact_success']) ?>
<?php else: ?>
<h1>Contact Us</h1>
<p class="text-muted">This is our contact page...</p>
<hr>
<div class="error-msg alert alert-danger cnt-error">
<p>Please fill in all required fields.</p>
</div>
<form id="contact_form" action="<?= site_url() ?>contact/save" method="post">
<div class="form-group">
<label for="name" class="form-label">Your Name*</label>
<input id="cnt_name" type="text" class="form-control" name="name" placeholder="Your Name">
</div>
<div class="form-group">
<label for="email" class="form-label">Your Email*</label>
<input id="cnt_email" type="text" class="form-control" name="email" placeholder="user#example.com">
</div>
<div class="form-group">
<label for="subject" class="form-label">Subject*</label>
<input id="cnt_subject" type="text" class="form-control" name="subject" placeholder="This website rocks">
</div>
<div class="form-group">
<label for="message" class="form-label">Comments*</label>
<textarea id="cnt_message" class="form-control" name="message" rows="10" placeholder="Enter a few questions in here..."></textarea>
</div>
<div class="form-group">
<button class="btn btn-primary">Submit</button>
Cancel
</div>
<!-- /.form-group -->
</form>
<?php endif ?>
</div>
</div>
</div>
</div>
</div>
</div>
<!-- /.section-md -->

Answer 1

I think you had margin in your
Let's try this code
body{
margin: 0;
}