Loading span styling

I’m testing the lite version before buying the pro plugin. All seems good, but I have a small issue with the styling of the loading span.

I’ve selected underline white and left styling as default, but when I view the search box on my site, there is a black background within the search box (<span class=”loading”>) that covers the placeholder of the search box. It looks like it’s the like plugin CSS that is controlling this too, rather than any theme or other plugin CSS taking over. From style.basic.css:
div.asl_m .probox .proinput .loading {
width:32px;
background:#000;
height:100%;
box-shadow:none;
}

Before I go editing the CSS to resolve this, I wanted to check what it’s used for and why it is there? Changing the colour and width doesn’t seem to effect anything of the functionality of the search