XML : Check which xml file you are in with xsl

I have a navigation bar in my html file which has links to different pages. I have an xsl for 2 xml files called luxury.xml and budget.xml. My navbar needs to highlight the button of whichever file im in i.e. if im on my homepage, the home button will be highlighted. I'm not sure how in xsl I distinguish between whether I'm on budget.xml or luxury.xml to highlight the respective button in the navbar. If somebody could tell me how to do that it would be much appreciated. My navbar looks like this

  <nav>       <ul id="navbar">          <li><a class="buttons" id="using" href="index.html">Home</a></li>           <li><a class="buttons" href="luxury.xml">Luxury</a></li>          <li><a class="buttons" href="budget.xml">Budget</a></li>          <li><a class="buttons" href="survey.html">Survey</a></li>      </ul>     </nav>     

id="using" is the id in my css that changes the colour of the button.