diff --git a/style/main.css b/style/main.css
index 6f98961..46d6f49 100644
--- a/style/main.css
+++ b/style/main.css
@@ -153,17 +153,17 @@ main.loading, main.not-found {
   position: relative;
   max-width: none;
   width: 100%;
-  /* lvh (large viewport height), not svh: svh pins to the *smallest*
-     viewport (toolbar visible), which never grows once the browser
-     auto-collapses its toolbar on the first scroll - so the actual
-     visible screen becomes taller than this box, and the content
-     below appears to snap into the newly-revealed space the moment
-     that happens. lvh pins to the toolbar-collapsed size instead,
-     matching the settled state scrolling actually lands on, so
-     there's no gap to reveal. (svh is the right choice for the
-     opposite case - a fixed element that must never be hidden behind
-     the toolbar - not a hero at the top of a scrolling page.)
-     Plain-vh fallback declared first - an engine without lvh support
+  /* svh (small viewport height): a fixed, stable length - computed
+     once, never recalculated mid-scroll as mobile Safari's address
+     bar hides/shows, unlike plain vh/dvh on some engines. Pinned to
+     the *smallest* possible viewport (toolbar visible) so the box
+     never needs to grow into space the toolbar might reclaim.
+     yes.js's canvas measures this box's own rendered rect (not
+     window.innerWidth/innerHeight) via ResizeObserver, so the canvas
+     always matches whatever height this resolves to - the two can't
+     disagree, which is what was actually causing the content below to
+     visibly jump.
+     Plain-vh fallback declared first - an engine without svh support
      ignores the invalid second line rather than falling through to
      auto height, which would collapse this to the height of its
      in-flow content and clip the canvas via overflow:hidden below. */
diff --git a/yes.js b/yes.js
index bebf45a..9c9ce3c 100644
--- a/yes.js
+++ b/yes.js
@@ -42,6 +42,7 @@ export class RasterizedYES {
         this.wiggleAmount = 0.5;
 
         this.setupCanvas();
+        this.setupResizeObserver();
         this.setupMouseTracking();
         this.setupClickHandler();
         this.rasterizeText();
@@ -51,15 +52,24 @@ export class RasterizedYES {
 
     stop() {
         this.destroyed = true;
-        if (this._resizeHandler) {
-            window.removeEventListener('resize', this._resizeHandler);
+        if (this._resizeObserver) {
+            this._resizeObserver.disconnect();
         }
     }
 
+    // Measures the canvases' own containing box (.hero-canvas, which
+    // tracks .hero-yes via inset:0) rather than window.innerWidth/
+    // innerHeight. window.innerHeight is the live viewport - it moves
+    // as mobile Safari's address bar hides/shows on scroll, which
+    // doesn't itself match whatever fixed value .hero-yes's CSS height
+    // is pinned to. Sizing the canvas off the box's own rect instead
+    // means the two can never disagree, whichever viewport unit ends
+    // up governing that box.
     setupCanvas() {
         const pixelRatio = window.devicePixelRatio || 1;
-        const width = window.innerWidth;
-        const height = window.innerHeight;
+        const rect = this.rasterCanvas.parentElement.getBoundingClientRect();
+        const width = rect.width;
+        const height = rect.height;
 
         this.rasterCanvas.style.width = width + 'px';
         this.rasterCanvas.style.height = height + 'px';
@@ -77,27 +87,27 @@ export class RasterizedYES {
         this.displayWidth = width;
         this.displayHeight = height;
         this.pixelRatio = pixelRatio;
+    }
 
-        if (!this._resizeHandler) {
-            // Mobile browsers change window.innerHeight (not width) as
-            // the address bar hides/shows during scroll, firing a
-            // `resize` with no real layout change to react to.
-            // Genuine resizes (orientation change, desktop window
-            // drag) always change the width too, so gate the redraw
-            // on that instead of reacting to every resize event.
-            this._resizeHandler = () => {
-                if (window.innerWidth === this.displayWidth) return;
-                this.setupCanvas();
-                this.rasterizeText();
-            };
-            window.addEventListener('resize', this._resizeHandler);
-        }
+    // ResizeObserver reacts to the container's box actually changing
+    // size - a fixed-height box (svh, lvh, or plain px) never fires
+    // this at all during the address-bar animation, so there's no
+    // need for the old "only redraw if width changed" heuristic that
+    // guessed at which resize events were real.
+    setupResizeObserver() {
+        this._resizeObserver = new ResizeObserver((entries) => {
+            const { width, height } = entries[0].contentRect;
+            if (width === this.displayWidth && height === this.displayHeight) return;
+            this.setupCanvas();
+            this.rasterizeText();
+        });
+        this._resizeObserver.observe(this.rasterCanvas.parentElement);
     }
 
     setupMouseTracking() {
         const updatePosition = (clientX, clientY) => {
-            this.mouseX = clientX / window.innerWidth;
-            this.mouseY = clientY / window.innerHeight;
+            this.mouseX = clientX / this.displayWidth;
+            this.mouseY = clientY / this.displayHeight;
             this.containmentStrength = 0.1 + (this.mouseX * 0.9);
             this.wiggleAmount = 0.1 + (this.mouseY * 1.9);
         };