If you're working with smaller screens, consider dividing the content into groups of two for a more visually appealing layout. Adjusting your CSS code may be necessary to remove any offset that could affect the overall look:
Check out this CodePen example for reference.
<div class="row buffer-top">
<div class="col-sm-3 col-xs-6 text-center">
<div class="thumbnail">
<span class="fa-stack fa-4x"><i class="fa fa-circle fa-stack-2x icon-siteAccess"></i><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-clipboard fa-stack-1x"></i></span>
<div class="caption">
<h3>Site Access Controllers</h3>
<p><strong>Location:</strong> UK-wide</p>
<p><a href="portals/0/resources/pdf/placeholder.pdf" target="blank" class="btn btn-default" role="button">More info</a><a href="mailto:<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="93f9fcf2f8fafebdf8f2f8f2f6fad3f9f2f1f6e1fcf0fcfde0e6ffe7fafdf4bdf0fcfe">[email protected]</a>" target="_blank"class="btn btn-default" role="button">Apply</a></p>
</div>
</div>
</div>
<div class="col-sm-3 col-xs-6 text-center">
<div class="thumbnail">
<span class="fa-stack fa-4x"><i class="fa fa-circle fa-stack-2x icon-developers"></i><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-code fa-stack-1x"></i></span>
<div class="caption">
<h3>Software Developers</h3>
<p><strong>Location:</strong> Tunbridge Wells</p>
<p><a href="portals/0/resources/pdf/softwarePlaceholder.pdf" target="blank" class="btn btn-default" role="button">More info</a><a href="mailto:<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="e3898c82888a8ecd88828882886aaabbabcccaaba1aabba8ada6cccacbdaf9a5aebecbcdaadfbfbcbecdbbebfcbb8cefdcbcacc">[email protected]</a>" target="_blank" class="btn btn-default" role="button">Apply</a></p>
</div>
</div>
</div>
<div class="col-sm-3 col-xs-6 text-center">
<div class="thumbnail">
<span class="fa-stack fa-4x"><i class="fa fa-circle fa-stack-2x icon-office"></i><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-building-o fa-stack-1x"></i></span>
<div class="caption">
<h3>Site Access Manager</h3>
<p><strong>Location:</strong> UK-wide</p>
<p><a href="portals/0/resources/pdf/hOfficePlaceholder.pdf" target="blank" class="btn btn-default" role="button">More info</a><a href="mailto:<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="d0babfb1bbb9bdfebbb1bbb1b5b990bab1b2b5a2bfb3bfbea3a5bca4b9beb7feb3bfbd">[email protected]</a>" target="_blank" class="btn btn-default" role="button">Apply</a></p>
</div>
</div>
</div>
<div class="col-sm-3 col-xs-6 text-center">
<div class="thumbnail">
<span class="fa-stack fa-4x"><i class="fa fa-circle fa-stack-2x icon-consultant"></i><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-question fa-stack-1x"></i></span>
<div class="caption">
<h3>Site Consultants</h3>
<p><strong>Location:</strong> UK-Wide</p>
<p><a href="portals/0/resources/pdf/consultantPlaceholder.pdf" target="blank" class="btn btn-default" role="button">More info</a><a href="mailto:<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="9cf6f3fdf7f5f1b2f7fdf7fdf9f5dcf6fdfef9eef3fff3f2efe9f0e8f5f2fbb2fff3f1">[email protected]</a>" target="_blank" class="btn btn-default" role="button">Apply</a></p>
</div>
</div>
</div>
</div>
To style the thumbnails in CSS:
.thumbnail {
margin: 0 auto 20px auto;
width: 200px;
height: 350px;
border: 2px solid black;
}