first commit

script.js

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+// CDJ-900NXS Mods — small helpers: theme toggle, before/after slider, docs TOC highlight.
+(function () {
+  var root = document.documentElement;
+
+  function storedTheme() {
+    try { return localStorage.getItem('theme'); } catch (e) { return null; }
+  }
+  var t = storedTheme();
+  if (t === 'light' || t === 'dark') root.setAttribute('data-theme', t);
+
+  document.addEventListener('DOMContentLoaded', function () {
+    var btn = document.querySelector('.theme-btn');
+    function label() {
+      if (btn) btn.textContent = root.getAttribute('data-theme') === 'light' ? '☾' : '☀';
+    }
+    label();
+    if (btn) btn.addEventListener('click', function () {
+      var next = root.getAttribute('data-theme') === 'light' ? 'dark' : 'light';
+      root.setAttribute('data-theme', next);
+      try { localStorage.setItem('theme', next); } catch (e) { /* private mode */ }
+      label();
+    });
+
+    // before / after
+    document.querySelectorAll('.compare').forEach(function (box) {
+      var range = box.querySelector('input[type="range"]');
+      if (!range) return;
+      function set() { box.style.setProperty('--pos', range.value + '%'); }
+      range.addEventListener('input', set);
+      set();
+    });
+
+    // docs: highlight the section in view
+    var links = Array.prototype.slice.call(document.querySelectorAll('.toc a[href^="#"]'));
+    if (links.length && 'IntersectionObserver' in window) {
+      var byId = {};
+      links.forEach(function (a) { byId[a.getAttribute('href').slice(1)] = a; });
+      var obs = new IntersectionObserver(function (entries) {
+        entries.forEach(function (e) {
+          if (e.isIntersecting && byId[e.target.id]) {
+            links.forEach(function (a) { a.classList.remove('active'); });
+            byId[e.target.id].classList.add('active');
+          }
+        });
+      }, { rootMargin: '-80px 0px -70% 0px' });
+      Object.keys(byId).forEach(function (id) {
+        var el = document.getElementById(id);
+        if (el) obs.observe(el);
+      });
+    }
+  });
+})();