diff --git a/website/templates/site.js b/website/templates/site.js
index 090e90cc..d639c7fb 100644
--- a/website/templates/site.js
+++ b/website/templates/site.js
@@ -28,6 +28,169 @@
       location.replace('#/notes/' + encodeURIComponent(route) + (hash.includes('?') ? '?' + hash.split('?').slice(1).join('?') : ''));
     }
   }
+  var stopSpy = null;
+  // 高频小节：构建网站时把标题和目录中的 🔥 换成了空的 span（hot-1 为一个火焰，hot-2 为两个），这里画出小火焰，侧边栏中也显示同样的标记
+  var FLAME = '<svg viewBox="0 0 16 20" aria-hidden="true"><path class="o" d="M8 .6C9.2 4.4 14 6.8 14 12.4A6 6 0 0 1 2 12.4C2 9.2 3.6 7.3 4.9 6.1C5 8.2 5.8 9.5 6.9 9.9C6.2 6.6 7.1 3.2 8 .6Z"/>' +
+    '<path class="i" d="M8 11C8.7 12.8 10.6 13.6 10.6 15.7A2.6 2.6 0 0 1 5.4 15.7C5.4 14.3 6.3 13.4 7 12.8C7.1 13.8 7.5 14.4 8.1 14.5C7.7 13.3 7.7 12.1 8 11Z"/></svg>';
+  function hotLevel(node) {
+    return node.classList.contains('hot-2') ? 2 : 1;
+  }
+  function fillHot(node, level) {
+    node.title = level === 2 ? '面试中最常问' : '面试中常被问到';
+    node.setAttribute('role', 'img');
+    node.setAttribute('aria-label', level === 2 ? '高频' : '常问');
+    node.innerHTML = level === 2 ? FLAME + FLAME : FLAME;
+  }
+  function hotBadge(level) {
+    var badge = document.createElement('span');
+    badge.className = 'hot hot-' + level;
+    fillHot(badge, level);
+    return badge;
+  }
+  function drawHot(section) {
+    section.querySelectorAll('.hot:empty').forEach(function (node) { fillHot(node, hotLevel(node)); });
+  }
+
+  // 步骤动图：GitHub 上直接播放 GIF；网站上用同一个 GIF 的各帧（构建时拆出）做播放器，可以暂停、逐步查看
+  function stepAnimations(section) {
+    var map = window.CS_NOTES_ANIMATIONS || {};
+    section.querySelectorAll('img').forEach(function (img) {
+      if (img.dataset.anim) return;
+      var key;
+      try { key = decodeURI(new URL(img.getAttribute('src'), location.href).pathname); } catch (error) { return; }
+      var anim = map[key];
+      if (!anim) return;
+      img.dataset.anim = '1';
+      anim.frames.forEach(function (src) { new Image().src = src; });
+      var index = 0, timer = null, playing = false, visible = false;
+      var bar = document.createElement('div');
+      bar.className = 'anim-bar';
+      bar.innerHTML = '<button type="button" data-step="-1" aria-label="上一步">上一步</button>' +
+        '<button type="button" data-play aria-label="暂停">暂停</button>' +
+        '<button type="button" data-step="1" aria-label="下一步">下一步</button><span class="anim-count"></span>';
+      var playButton = bar.querySelector('[data-play]'), count = bar.querySelector('.anim-count');
+      function show(i) {
+        index = (i + anim.frames.length) % anim.frames.length;
+        img.src = anim.frames[index];
+        count.textContent = (index + 1) + ' / ' + anim.frames.length;
+      }
+      function schedule() {
+        clearTimeout(timer);
+        if (playing && visible) timer = setTimeout(function () { show(index + 1); schedule(); }, anim.durations[index]);
+      }
+      function setPlaying(value) {
+        playing = value;
+        playButton.textContent = value ? '暂停' : '播放';
+        playButton.setAttribute('aria-label', playButton.textContent);
+        schedule();
+      }
+      bar.addEventListener('click', function (event) {
+        var button = event.target.closest('button');
+        if (!button) return;
+        if (button.hasAttribute('data-play')) { setPlaying(!playing); return; }
+        setPlaying(false);
+        show(index + Number(button.dataset.step));
+      });
+      img.after(bar);
+      show(0);
+      setPlaying(!window.matchMedia('(prefers-reduced-motion: reduce)').matches);
+      if ('IntersectionObserver' in window) {
+        new IntersectionObserver(function (entries) {
+          visible = entries[entries.length - 1].isIntersecting;
+          schedule();
+        }, { threshold: 0.25 }).observe(img);
+      } else {
+        visible = true;
+        schedule();
+      }
+    });
+  }
+
+  function articleToc(vm) {
+    // 侧边栏中显示当前文章的二、三级标题：文章在侧边栏中时挂在它下面，否则放在侧边栏顶部
+    var nav = document.querySelector('.sidebar-nav');
+    var section = document.querySelector('.markdown-section');
+    if (stopSpy) { stopSpy(); stopSpy = null; }
+    if (!nav || !section) return;
+    nav.querySelectorAll('.page-toc, .page-toc-block').forEach(function (node) { node.remove(); });
+    // Docsify 按前缀匹配当前项：“首页”的 #/ 会匹配所有文章，地址带 ?id= 时又匹配不到，这里按完整路径重新标记
+    var target = decode('#' + vm.route.path), active = null;
+    nav.querySelectorAll('li > a').forEach(function (link) {
+      var same = !active && decode((link.getAttribute('href') || '').split('?')[0]) === target;
+      link.parentNode.classList.toggle('active', same);
+      if (same) active = link.parentNode;
+    });
+    if (vm.route.path === '/') return;
+    drawHot(section);
+    var heads = Array.from(section.querySelectorAll('h2[id], h3[id]'));
+    if (heads.length < 2) return;
+    var route = '#' + encodedRoute(vm.route.path) + '?id=';
+    var root = document.createElement('ul');
+    root.className = 'page-toc';
+    var group = null, flat = false, links = {};
+    heads.forEach(function (heading) {
+      var title = heading.textContent.trim();
+      if (heading.tagName === 'H3' && (flat || !group)) return;
+      var li = document.createElement('li');
+      var a = document.createElement('a');
+      a.href = route + encodeURIComponent(heading.id);
+      a.textContent = a.title = title;
+      li.appendChild(a);
+      var mark = heading.querySelector('.hot');
+      if (mark) a.appendChild(hotBadge(hotLevel(mark)));
+      links[heading.id] = li;
+      if (heading.tagName === 'H2') {
+        root.appendChild(li);
+        group = li;
+        flat = /^(附录|参考资料)/.test(title);
+      } else {
+        var sub = group.querySelector(':scope > ul');
+        if (!sub) {
+          sub = document.createElement('ul');
+          group.appendChild(sub);
+          group.classList.add('has-sub');
+        }
+        sub.appendChild(li);
+      }
+    });
+    if (active) {
+      active.appendChild(root);
+    } else {
+      var block = document.createElement('div');
+      block.className = 'page-toc-block';
+      var name = document.createElement('p');
+      name.className = 'page-toc-title';
+      name.textContent = (section.querySelector('h1') || {}).textContent || decode(vm.route.path.split('/').pop());
+      block.appendChild(name);
+      block.appendChild(root);
+      nav.insertBefore(block, nav.firstChild);
+    }
+    var sidebar = document.querySelector('.sidebar');
+    var pending = false;
+    function update() {
+      pending = false;
+      var current = null;
+      for (var i = 0; i < heads.length; i++) {
+        if (heads[i].getBoundingClientRect().top > 90) break;
+        if (links[heads[i].id]) current = links[heads[i].id];
+      }
+      root.querySelectorAll('li.current, li.open').forEach(function (li) { li.classList.remove('current', 'open'); });
+      if (!current) return;
+      current.classList.add('current');
+      var top = current.parentNode === root ? current : current.parentNode.parentNode;
+      top.classList.add('open');
+      if (sidebar) {
+        var offset = current.getBoundingClientRect().top - sidebar.getBoundingClientRect().top;
+        if (offset < 60 || offset > sidebar.clientHeight - 60) sidebar.scrollTop += offset - sidebar.clientHeight / 3;
+      }
+    }
+    function onScroll() {
+      if (!pending) { pending = true; requestAnimationFrame(update); }
+    }
+    window.addEventListener('scroll', onScroll, { passive: true });
+    stopSpy = function () { window.removeEventListener('scroll', onScroll); };
+    update();
+  }
   preserveLegacyLinks();
   window.addEventListener('hashchange', preserveLegacyLinks);
   window.$docsify = {
@@ -61,6 +224,8 @@
         var heading = document.querySelector('.markdown-section h1, .markdown-section h2');
         document.title = (vm.route.path === '/' || !heading ? 'CS-Notes' : heading.textContent.trim() + ' · CS-Notes') + ' · CyC2018';
         configureImages(document.querySelector('.markdown-section'), vm.route.path === '/');
+        stepAnimations(document.querySelector('.markdown-section'));
+        articleToc(vm);
         document.querySelectorAll('.article-toc').forEach(function (toc) {
           toc.open = window.matchMedia('(min-width: 769px)').matches;
         });