Adding a fixed banner over showcase image?

Hi, I'm trying to add a banner over the showcase image to my site, much like this example:
http://www.sharps.co.uk

Also, it's important that it's responsive.

Is there an easy way to go about doing this? My website being:
http://www.mark-nichols.net

Thanks!

This should help get you started in the right direction.

HTML

<section id="hero">
    <div class="row">
       ...
    </div>
    <div class='hero__overlay">Overlay content</div>
</section>

CSS

#hero { position: relative; }
.hero__overlay { position: absolute; top: 0; left: 10px; } /* Change top & left to whatever works best */