Those flags are in SVG format. The problem is that they don't show up!
If I put them anywhere else everything is working perfectly fine... I am trying to make a dropdown menu for selecting language.
Thank you!

<select name="language">
    <option value="bg"><span class="flag flag-bel flag-10x"></span>Belgium</option>
    <option value="fr"><span class="flag flag-fra flag-10x"></span>France</option>
 </select>