frontend/app/trees/[id]/tree/chart.css

@@ -381,9 +381,25 @@
   color: rgb(255, 251, 220);
   background-color: rgba(255, 251, 220, 0);
   border-radius: 50%;
-  padding: 2px;
+  padding: 2px 4px;
+  font-weight: 600;
+  cursor: pointer;
   transition: color 0.2s ease-in-out, background-color 0.2s ease-in-out;
 }
+.f3 .f3-card-duplicate-tag:hover {
+  background-color: rgba(255, 251, 220, 0.9);
+  color: #000;
+}
+
+/* Click the ×N badge → every copy of that person flashes (see tree/page.tsx). */
+@keyframes f3-card-flash {
+  0%, 100% { outline-color: rgba(160, 106, 66, 0); }
+  30%, 70% { outline-color: rgba(160, 106, 66, 1); }
+}
+.f3 .f3-card-flash .card-inner {
+  outline: 4px solid rgba(160, 106, 66, 1);
+  animation: f3-card-flash 0.55s ease-in-out 3;
+}
 
 .f3 .f3-card-duplicate-hover div.card-inner {
   transform: translate(0, -2px);

frontend/app/trees/[id]/tree/page.tsx

@@ -252,6 +252,36 @@ export default function TreePage() {
     [mode],
   );
 
+  // Click the "×N" duplicate badge on a card to flash every copy of that person
+  // in the current view. They're the same record drawn in two places (a shared
+  // ancestor, or an intermarriage). Delegated on the container so it survives
+  // chart rebuilds; capture-phase + stopPropagation so it doesn't also recenter.
+  useEffect(() => {
+    const el = containerRef.current;
+    if (!el) return;
+    type Bound = Element & { __data__?: { data?: { id?: string } } };
+    const idOf = (node: Element | null) => (node as Bound | null)?.__data__?.data?.id;
+    function onClick(e: MouseEvent) {
+      const tag = (e.target as HTMLElement).closest?.(".f3-card-duplicate-tag");
+      if (!tag) return;
+      e.preventDefault();
+      e.stopPropagation();
+      const id = idOf(tag.closest(".card_cont"));
+      if (!id) return;
+      el!.querySelectorAll(".card_cont").forEach((cont) => {
+        if (idOf(cont) !== id) return;
+        const card = cont.querySelector(".card") as HTMLElement | null;
+        if (!card) return;
+        card.classList.remove("f3-card-flash");
+        void card.offsetWidth; // restart the animation on repeat clicks
+        card.classList.add("f3-card-flash");
+        window.setTimeout(() => card.classList.remove("f3-card-flash"), 1900);
+      });
+    }
+    el.addEventListener("click", onClick, true);
+    return () => el.removeEventListener("click", onClick, true);
+  }, []);
+
   // Mirror the focused person into the URL (?focus=…) so navigating away and
   // back — or sharing the link — keeps the tree centered where you left it.
   // `replace` (not push) so each recenter doesn't pile up in browser history.
@@ -402,11 +432,46 @@ export default function TreePage() {
         />
       )}
 
-      <p className="text-sm text-[var(--muted)]">
-        {mode === "fan"
-          ? "Click an ancestor to recenter the fan."
-          : "Drag to pan · scroll to zoom · click a person to recenter."}
-      </p>
+      <div className="flex flex-wrap items-center gap-x-3 gap-y-1 text-sm text-[var(--muted)]">
+        <span>
+          {mode === "fan"
+            ? "Click an ancestor to recenter the fan."
+            : "Drag to pan · scroll to zoom · click a person to recenter."}
+        </span>
+        {mode !== "fan" && (
+          <div className="group relative">
+            <button
+              type="button"
+              className="underline decoration-dotted underline-offset-2 hover:text-bronze focus-visible:text-bronze focus-visible:outline-none"
+            >
+              Legend
+            </button>
+            <div className="invisible absolute bottom-full left-0 z-30 mb-2 w-80 rounded-lg border border-[var(--border)] bg-[var(--surface)] p-3 text-xs text-[var(--foreground)] opacity-0 shadow-lg transition-opacity group-hover:visible group-hover:opacity-100 group-focus-within:visible group-focus-within:opacity-100">
+              <ul className="space-y-2">
+                <li>
+                  <span className="font-semibold text-bronze">×N</span> on a card — this
+                  person appears N times in the current view. The same record is drawn in
+                  two places because they connect through more than one line (a shared
+                  ancestor, or an intermarriage).{" "}
+                  <span className="text-[var(--muted)]">Click the ×N to flash the other copies.</span>
+                </li>
+                <li className="flex flex-wrap items-center gap-x-2 gap-y-1">
+                  <span className="inline-flex items-center gap-1">
+                    <span className="inline-block h-2.5 w-2.5 rounded-sm" style={{ background: "rgb(120,159,172)" }} /> male
+                  </span>
+                  <span className="inline-flex items-center gap-1">
+                    <span className="inline-block h-2.5 w-2.5 rounded-sm" style={{ background: "rgb(196,138,146)" }} /> female
+                  </span>
+                  <span className="inline-flex items-center gap-1">
+                    <span className="inline-block h-2.5 w-2.5 rounded-sm" style={{ background: "lightgray" }} /> sex not set
+                  </span>
+                </li>
+                <li>Drag to pan, scroll to zoom, and click any card to recenter the tree on that person.</li>
+              </ul>
+            </div>
+          </div>
+        )}
+      </div>
     </div>
   );
 }