Show definition popups on mouseover

script.js

@@ -351,3 +351,142 @@ window.addEventListener("hashchange", () => {
     tocList?.querySelector(`a[href="#${id}"]`)?.scrollIntoView({ block: "nearest" });
   }
 });
+
+// Entry popup preview on hover
+const popup = document.createElement("div");
+popup.className = "entry-popup";
+popup.hidden = true;
+document.body.appendChild(popup);
+
+let hoverTimer = null;
+let closeTimer = null;
+const HOVER_DELAY = 500;
+const CLOSE_DELAY = 500;
+
+const getEntryContent = (id) => {
+  const titleEl = document.getElementById(id);
+  if (!titleEl) return null;
+
+  const allTitles = Array.from(document.querySelectorAll(".entry-title"));
+  const titleIndex = allTitles.indexOf(titleEl);
+  const nextTitle = allTitles[titleIndex + 1] || null;
+
+  const range = document.createRange();
+  range.setStartBefore(titleEl);
+  if (nextTitle) {
+    range.setEndBefore(nextTitle);
+  } else {
+    range.setEndAfter(contentEl.lastChild);
+  }
+
+  const content = range.cloneContents();
+
+  const clonedTitle = content.querySelector(".entry-title");
+  if (clonedTitle) {
+    clonedTitle.removeAttribute("id");
+  }
+
+  return content;
+};
+
+const positionPopup = (linkRect) => {
+  const pad = 8;
+  const popupRect = popup.getBoundingClientRect();
+  const vw = window.innerWidth;
+  const vh = window.innerHeight;
+
+  let top = linkRect.top - popupRect.height - pad;
+  let left = linkRect.left;
+
+  if (top < pad) {
+    top = linkRect.bottom + pad;
+  }
+
+  if (left + popupRect.width > vw - pad) {
+    left = vw - popupRect.width - pad;
+  }
+
+  if (left < pad) {
+    left = pad;
+  }
+
+  popup.style.top = `${top}px`;
+  popup.style.left = `${left}px`;
+};
+
+const showPopup = (link) => {
+  const href = link.getAttribute("href");
+  if (!href?.startsWith("#entry-")) return;
+
+  const id = href.slice(1);
+  const content = getEntryContent(id);
+  if (!content) return;
+
+  popup.innerHTML = "";
+  popup.appendChild(content);
+  popup.hidden = false;
+
+  popup.style.top = "0";
+  popup.style.left = "0";
+  popup.classList.remove("visible");
+
+  requestAnimationFrame(() => {
+    popup.scrollTop = 0;
+    const linkRect = link.getBoundingClientRect();
+    positionPopup(linkRect);
+    popup.classList.add("visible");
+  });
+};
+
+const hidePopup = () => {
+  popup.classList.remove("visible");
+  setTimeout(() => {
+    if (!popup.classList.contains("visible")) {
+      popup.hidden = true;
+    }
+  }, 200);
+};
+
+const clearTimers = () => {
+  clearTimeout(hoverTimer);
+  clearTimeout(closeTimer);
+  hoverTimer = null;
+  closeTimer = null;
+};
+
+const isEntryLink = (el) =>
+  el?.tagName === "A" &&
+  el.classList.contains("entry-link") &&
+  el.getAttribute("href")?.startsWith("#entry-");
+
+contentEl?.addEventListener("mouseenter", (e) => {
+  if (isMobile()) return;
+  if (!isEntryLink(e.target)) return;
+
+  clearTimers();
+  hoverTimer = setTimeout(() => showPopup(e.target), HOVER_DELAY);
+}, true);
+
+contentEl?.addEventListener("mouseleave", (e) => {
+  if (isMobile()) return;
+  if (!isEntryLink(e.target)) return;
+
+  clearTimers();
+  closeTimer = setTimeout(hidePopup, CLOSE_DELAY);
+}, true);
+
+popup.addEventListener("mouseenter", () => {
+  clearTimers();
+});
+
+popup.addEventListener("mouseleave", () => {
+  clearTimers();
+  closeTimer = setTimeout(hidePopup, CLOSE_DELAY);
+});
+
+popup.addEventListener("click", (e) => {
+  if (e.target.tagName === "A") {
+    clearTimers();
+    hidePopup();
+  }
+});

style.css

@@ -267,6 +267,52 @@ body.toc-collapsed .toc-toggle::before {
   grid-template-columns: 0 minmax(0, 1fr);
 }
 
+/* Entry popup preview */
+.entry-popup {
+  position: fixed;
+  z-index: 300;
+  max-width: min(420px, 90vw);
+  max-height: min(320px, 60vh);
+  overflow-y: auto;
+  background: var(--paper);
+  border-radius: 12px;
+  padding: 16px 20px;
+  box-shadow:
+    0 8px 32px var(--shadow),
+    0 2px 8px rgba(45, 34, 26, 0.1);
+  border: 1px solid rgba(70, 50, 36, 0.15);
+  font-size: 0.95rem;
+  line-height: 1.55;
+  opacity: 0;
+  transform: translateY(4px);
+  transition:
+    opacity 0.2s ease,
+    transform 0.2s ease;
+  pointer-events: none;
+}
+
+.entry-popup.visible {
+  opacity: 1;
+  transform: translateY(0);
+  pointer-events: auto;
+}
+
+.entry-popup .entry-title {
+  animation: none;
+}
+
+.entry-popup p {
+  margin: 0 0 0.75em;
+}
+
+.entry-popup p:last-child {
+  margin-bottom: 0;
+}
+
+.entry-popup .entry-link {
+  pointer-events: auto;
+}
+
 @media (max-width: 700px) {
   .page,
   .hero,