language switcher, flags only

Hi,
Any idea of how can we have flags only with shortcode using css?

html output exemple shortcode

<ul class="bogo-language-switcher">
 <li class="en-US en first">
  <span class="bogoflags bogoflags-us"></span> 
   <a rel="alternate" hreflang="en-US" href="/en/" title="English (United States)">English (United States)</a>
 </li>
 <li class="fr-FR fr current last">
  <span class="bogoflags bogoflags-fr"></span> Fran?ais
 </li>
</ul>