DistroHopper/src/toggle.html

<button class="theme-toggle" onclick="toggleTheme()">🌓</button>
<script>
  function toggleTheme(){
    const html=document.documentElement;
    const current=html.getAttribute("data-theme")||"dark";
    const next=current==="dark"?"light":"dark";
    html.setAttribute("data-theme",next);
    localStorage.setItem("theme",next)
  }
  (function(){
    const saved=localStorage.getItem("theme")||"dark";
    document.documentElement.setAttribute("data-theme",saved)
  })();
</script>