How do I edit a file input in CSS?

Question

I am using twitter bootstrap for a project and want to create a dropdown menu and have the list items act as a file upload but cant seem to edit it in such a way!I do not want a button in my dropdown menu nor do I want a separate button or entity that shelters the button. I want a dropdown menu where the list item acts as a file upload button and is styled as such, below is the base html code using bootstrap 3.0

<ul>
    <li>
        <input type="file">
            <span class="glyphicon glyphicon-file">
            </span>
            File Upload
    </li>
</ul>

I know how to edit it to be a button but am not sure how to make it so it looks like a regular <li> but also act as the file input! Is this even possible?