Explainer preview: always light, no light/dark button

- the light/dark button is removed (owner: start light and stay light)
- the pages stay in the light theme also on phones set to dark mode

preview-2a86b5/index.html

@@ -402,7 +402,6 @@ svg.tips .tip{opacity:1}
     <div class="langs" role="group" aria-label="Language"><button type="button" data-lang="en">EN</button><button type="button" data-lang="it">IT</button><button type="button" data-lang="es">ES</button></div>
     <span class="sndhint" id="sndhint" data-k="tapSound" hidden>tocca per il suono</span>
     <button class="snd" id="mus" type="button" data-t="music" aria-pressed="true"><svg viewBox="0 0 24 24" width="18" height="18" aria-hidden="true"><path d="M9 17V5l11-2v12" fill="none" stroke="currentColor" stroke-width="2" stroke-linejoin="round"/><circle cx="6.5" cy="17.5" r="2.8" fill="currentColor"/><circle cx="17.5" cy="15.5" r="2.8" fill="currentColor"/><path class="mute" d="M3 3l18 18" fill="none" stroke="currentColor" stroke-width="2.2" stroke-linecap="round"/></svg></button>
-    <button class="snd" id="thm" type="button" title="Light / dark" aria-label="Light / dark" onclick="var r=document.documentElement;r.setAttribute('data-theme',r.getAttribute('data-theme')==='dark'?'light':'dark')"><svg viewBox="0 0 24 24" width="18" height="18" aria-hidden="true"><circle cx="12" cy="12" r="8" fill="none" stroke="currentColor" stroke-width="2"/><path d="M12 4a8 8 0 0 1 0 16z" fill="currentColor"/></svg></button>
     <button class="snd" id="snd" type="button" data-t="sound" aria-pressed="true"><svg viewBox="0 0 24 24" width="18" height="18" aria-hidden="true"><path d="M4 9h4l5-4v14l-5-4H4z" fill="currentColor"/><path class="wave" d="M16 8.5a5 5 0 0 1 0 7M18.5 6a8.5 8.5 0 0 1 0 12" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round"/><path class="mute" d="M16 9l5 6M21 9l-5 6" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round"/></svg></button>
     </div>
   </div>