diff --git a/desktop/src/features/messages/lib/rowHeightEstimate.test.mjs b/desktop/src/features/messages/lib/rowHeightEstimate.test.mjs
index dc33da4f8..50e7c93ac 100644
--- a/desktop/src/features/messages/lib/rowHeightEstimate.test.mjs
+++ b/desktop/src/features/messages/lib/rowHeightEstimate.test.mjs
@@ -90,13 +90,13 @@ test("estimateRowHeight: bare URL line adds a preview card", () => {
   assert.ok(withUrl > withoutUrl + 50, `url ${withUrl} vs ${withoutUrl}`);
 });
 
-test("timelineRowReserveStyle: message item yields containIntrinsicSize", () => {
+test("timelineRowReserveStyle: message item yields rem containIntrinsicSize", () => {
   const style = timelineRowReserveStyle({
     kind: "message",
     key: "k",
     entry: { message: msg({ body: "hi" }), summary: null },
   });
-  assert.match(String(style.containIntrinsicSize), /^auto \d+px$/);
+  assert.match(String(style.containIntrinsicSize), /^auto \d+(?:\.\d+)?rem$/);
 });
 
 test("timelineRowReserveStyle: divider is short fixed height", () => {
@@ -105,5 +105,5 @@ test("timelineRowReserveStyle: divider is short fixed height", () => {
     key: "k",
     headingTimestamp: 0,
   });
-  assert.equal(style.containIntrinsicSize, "auto 32px");
+  assert.equal(style.containIntrinsicSize, "auto 2rem");
 });
diff --git a/desktop/src/features/messages/lib/rowHeightEstimate.ts b/desktop/src/features/messages/lib/rowHeightEstimate.ts
index c979a8ad1..199be4060 100644
--- a/desktop/src/features/messages/lib/rowHeightEstimate.ts
+++ b/desktop/src/features/messages/lib/rowHeightEstimate.ts
@@ -175,5 +175,5 @@ export function timelineRowReserveStyle(
       : item.kind === "system"
         ? estimateRowHeight(item.entry.message)
         : DIVIDER_HEIGHT;
-  return { containIntrinsicSize: `auto ${height}px` };
+  return { containIntrinsicSize: `auto ${height / 16}rem` };
 }
diff --git a/desktop/tests/e2e/channels.spec.ts b/desktop/tests/e2e/channels.spec.ts
index 032d2ede9..ae97643ea 100644
--- a/desktop/tests/e2e/channels.spec.ts
+++ b/desktop/tests/e2e/channels.spec.ts
@@ -6,6 +6,7 @@ import {
   installMockBridge,
   openChannelBrowser,
 } from "../helpers/bridge";
+import { expectedScaledPx } from "../helpers/css";
 
 const GENERAL_CHANNEL_ID = "9a1657ac-f7aa-5db0-b632-d8bbeb6dfb50";
 const MOCK_IDENTITY_PUBKEY = "deadbeef".repeat(8);
@@ -276,7 +277,9 @@ async function expectSameLeftInset(
     throw new Error(`Could not measure ${firstTestId} against ${secondTestId}`);
   }
 
-  expect(Math.abs(firstBox.x - secondBox.x)).toBeLessThanOrEqual(4);
+  expect(Math.abs(firstBox.x - secondBox.x)).toBeLessThanOrEqual(
+    await expectedScaledPx(page.getByTestId(firstTestId), 4),
+  );
 }
 
 async function expectIntroSpacedAboveDayDivider(
@@ -325,9 +328,14 @@ async function expectIntroActionCardLayout(
   }
 
   expect(actionBox.height).toBeGreaterThan(actionBox.width);
-  expect(Math.round(actionBox.width)).toBe(220);
-  expect(Math.round(iconBox.width)).toBe(48);
-  expect(Math.round(iconBox.height)).toBe(48);
+  expect(Math.round(actionBox.width)).toBe(
+    Math.round(await expectedScaledPx(page.getByTestId(actionTestId), 220)),
+  );
+  const expectedIconSize = Math.round(
+    await expectedScaledPx(page.getByTestId(`${actionTestId}-icon`), 48),
+  );
+  expect(Math.round(iconBox.width)).toBe(expectedIconSize);
+  expect(Math.round(iconBox.height)).toBe(expectedIconSize);
   const introIconRadius = await page
     .getByTestId("message-channel-intro-icon")
     .evaluate((element) => window.getComputedStyle(element).borderRadius);
diff --git a/desktop/tests/e2e/custom-emoji.spec.ts b/desktop/tests/e2e/custom-emoji.spec.ts
index 42c7e707a..488e76bba 100644
--- a/desktop/tests/e2e/custom-emoji.spec.ts
+++ b/desktop/tests/e2e/custom-emoji.spec.ts
@@ -1,6 +1,7 @@
 import { expect, test } from "@playwright/test";
 
 import { installMockBridge } from "../helpers/bridge";
+import { expectedScaledPx } from "../helpers/css";
 
 // Custom-emoji end-to-end guard.
 //
@@ -271,14 +272,34 @@ test("reacting with a custom emoji renders via the loopback media proxy", async
       }),
     )
     .toBe("0");
+  const expectedInlineReactionButtonWidth = Math.round(
+    await expectedScaledPx(inlineAddReactionButton, 40),
+  );
+  const minExpectedInlineReactionButtonHeight = Math.round(
+    await expectedScaledPx(inlineAddReactionButton, 28),
+  );
   await expect
     .poll(() =>
       inlineAddReactionButton.evaluate((button) => {
         const rect = button.getBoundingClientRect();
-        return `${Math.round(rect.width)}x${Math.round(rect.height)}`;
+        return {
+          height: Math.round(rect.height),
+          width: Math.round(rect.width),
+        };
       }),
     )
-    .toBe("40x28");
+    .toEqual({
+      height: expect.any(Number),
+      width: expectedInlineReactionButtonWidth,
+    });
+  await expect
+    .poll(() =>
+      inlineAddReactionButton.evaluate((button) => {
+        const rect = button.getBoundingClientRect();
+        return Math.round(rect.height);
+      }),
+    )
+    .toBeGreaterThanOrEqual(minExpectedInlineReactionButtonHeight);
   await expect
     .poll(() =>
       inlineAddReactionButton.evaluate((button) => {
@@ -292,10 +313,24 @@ test("reacting with a custom emoji renders via the loopback media proxy", async
     .poll(() =>
       inlineAddReactionButton.evaluate((button) => {
         const rect = button.getBoundingClientRect();
-        return `${Math.round(rect.width)}x${Math.round(rect.height)}`;
+        return {
+          height: Math.round(rect.height),
+          width: Math.round(rect.width),
+        };
       }),
     )
-    .toBe("40x28");
+    .toEqual({
+      height: expect.any(Number),
+      width: expectedInlineReactionButtonWidth,
+    });
+  await expect
+    .poll(() =>
+      inlineAddReactionButton.evaluate((button) => {
+        const rect = button.getBoundingClientRect();
+        return Math.round(rect.height);
+      }),
+    )
+    .toBeGreaterThanOrEqual(minExpectedInlineReactionButtonHeight);
 
   // Toggle the reaction back off: click the pill, which fires remove_reaction
   // -> emits a kind:5 deletion targeting the reaction event. The pill must
diff --git a/desktop/tests/e2e/file-attachment.spec.ts b/desktop/tests/e2e/file-attachment.spec.ts
index 41eb55e52..ac3148630 100644
--- a/desktop/tests/e2e/file-attachment.spec.ts
+++ b/desktop/tests/e2e/file-attachment.spec.ts
@@ -47,7 +47,7 @@ test("upload a file and see a FileCard in the timeline", async ({ page }) => {
   // escapes the webview to the OS browser and hits a corporate CDN page.
   const card = page.getByTestId("file-card").last();
   await expect(card).toBeVisible();
-  await expectCornerRadiusPx(card, 16);
+  await expectCornerRadiusPx(card, 16, { scaleWithRootFont: true });
   await expectSmoothCorners(card);
   await expect(card).toContainText("quarterly-report.pdf");
 
diff --git a/desktop/tests/e2e/image-attachment-gallery.spec.ts b/desktop/tests/e2e/image-attachment-gallery.spec.ts
index df4cfc980..6df4eaacf 100644
--- a/desktop/tests/e2e/image-attachment-gallery.spec.ts
+++ b/desktop/tests/e2e/image-attachment-gallery.spec.ts
@@ -126,8 +126,10 @@ test("image bundle lightbox navigates as a gallery", async ({ page }) => {
 
   const triggers = row.getByTestId("message-image-lightbox-trigger");
   await expect(triggers).toHaveCount(3);
-  await expectCornerRadiusPx(triggers.first(), 16);
-  await expectCornerRadiusPx(triggers.first().locator("img"), 16);
+  await expectCornerRadiusPx(triggers.first(), 16, { scaleWithRootFont: true });
+  await expectCornerRadiusPx(triggers.first().locator("img"), 16, {
+    scaleWithRootFont: true,
+  });
   await expectSmoothCorners(triggers.first().locator("img"));
   await triggers.first().click();
 
@@ -137,7 +139,7 @@ test("image bundle lightbox navigates as a gallery", async ({ page }) => {
   const lightboxSurface = page
     .locator("[data-image-lightbox-frame] > div > div")
     .first();
-  await expectCornerRadiusPx(lightboxSurface, 16);
+  await expectCornerRadiusPx(lightboxSurface, 16, { scaleWithRootFont: true });
   await expectSmoothCorners(lightboxSurface);
   await expect(
     page.getByRole("button", { name: "Previous image" }),
@@ -174,6 +176,7 @@ test("image bundle lightbox navigates as a gallery", async ({ page }) => {
   await expectCornerRadiusPx(
     page.locator("[data-image-lightbox-frame] > div > div").first(),
     16,
+    { scaleWithRootFont: true },
   );
 
   expect(Math.abs(closingFrameBox.x - currentThumbnailBox.x)).toBeLessThan(2);
diff --git a/desktop/tests/e2e/messaging.spec.ts b/desktop/tests/e2e/messaging.spec.ts
index 1c7202125..85f843ba0 100644
--- a/desktop/tests/e2e/messaging.spec.ts
+++ b/desktop/tests/e2e/messaging.spec.ts
@@ -1,7 +1,11 @@
 import { expect, test, type Locator } from "@playwright/test";
 
 import { installMockBridge, TEST_IDENTITIES } from "../helpers/bridge";
-import { expectCornerRadiusPx, expectSmoothCorners } from "../helpers/css";
+import {
+  expectCornerRadiusPx,
+  expectSmoothCorners,
+  expectedScaledPx,
+} from "../helpers/css";
 import { openSettings } from "../helpers/settings";
 
 async function expectThreadReplyUnobscured(row: Locator) {
@@ -179,7 +183,7 @@ test("supported link previews keep the message link visible", async ({
   ).toBeVisible();
   const previewCard = row.locator('[data-link-preview="github-pull-request"]');
   await expect(previewCard).toBeVisible();
-  await expectCornerRadiusPx(previewCard, 16);
+  await expectCornerRadiusPx(previewCard, 16, { scaleWithRootFont: true });
   await expectSmoothCorners(previewCard);
 });
 
@@ -233,7 +237,9 @@ test("copy a rendered code block and paste it back as code", async ({
 
   const codeBlock = page.locator("[data-code-block]");
   await expect(codeBlock).toHaveCount(1);
-  await expectCornerRadiusPx(codeBlock.locator("pre"), 16);
+  await expectCornerRadiusPx(codeBlock.locator("pre"), 16, {
+    scaleWithRootFont: true,
+  });
   await expectSmoothCorners(codeBlock.locator("pre"));
 
   const copyButton = page.getByLabel("Copy code block");
@@ -647,7 +653,19 @@ test("opens a single-level thread panel with inline expansion", async ({
           return `${Math.round(rect.width)}x${Math.round(rect.height)}`;
         }),
     )
-    .toBe("24x24");
+    .toBe(
+      `${Math.round(
+        await expectedScaledPx(
+          rootSummaryRow.getByTestId("message-thread-summary-participant"),
+          24,
+        ),
+      )}x${Math.round(
+        await expectedScaledPx(
+          rootSummaryRow.getByTestId("message-thread-summary-participant"),
+          24,
+        ),
+      )}`,
+    );
   const summaryGeometry = await measureThreadSummaryGeometry(rootSummaryRow);
   expect(
     Math.abs(summaryGeometry.authorLeft - summaryGeometry.bodyLeft),
diff --git a/desktop/tests/e2e/video-attachment.spec.ts b/desktop/tests/e2e/video-attachment.spec.ts
index c4bc4c70b..ff9a894b5 100644
--- a/desktop/tests/e2e/video-attachment.spec.ts
+++ b/desktop/tests/e2e/video-attachment.spec.ts
@@ -253,7 +253,7 @@ test("video upload previews use poster frames and inline videos open review mode
 
   const inlinePlayer = page.getByTestId("video-player").last();
   const inlineSurface = inlinePlayer.locator("[data-smooth-corners]").first();
-  await expectCornerRadiusPx(inlineSurface, 16);
+  await expectCornerRadiusPx(inlineSurface, 16, { scaleWithRootFont: true });
   await expectSmoothCorners(inlineSurface);
   const inlineVideo = inlinePlayer.locator("video");
   await inlinePlayer.getByRole("button", { name: "Play video" }).click();
diff --git a/desktop/tests/helpers/css.ts b/desktop/tests/helpers/css.ts
index 0985fb788..0f0b586b5 100644
--- a/desktop/tests/helpers/css.ts
+++ b/desktop/tests/helpers/css.ts
@@ -1,8 +1,25 @@
 import { expect, type Locator } from "@playwright/test";
 
+export async function currentRootFontScale(locator: Locator) {
+  const rootFontSize = await locator.evaluate(() =>
+    Number.parseFloat(
+      window.getComputedStyle(document.documentElement).fontSize,
+    ),
+  );
+  return Number.isFinite(rootFontSize) ? rootFontSize / 16 : 1;
+}
+
+export async function expectedScaledPx(
+  locator: Locator,
+  pxAtDefaultScale: number,
+) {
+  return pxAtDefaultScale * (await currentRootFontScale(locator));
+}
+
 export async function expectCornerRadiusPx(
   locator: Locator,
   expectedRadiusPx: number,
+  options: { scaleWithRootFont?: boolean } = {},
 ) {
   const measurement = await locator.evaluate((element) => {
     const style = window.getComputedStyle(element);
@@ -65,13 +82,18 @@ export async function expectCornerRadiusPx(
       className: element.getAttribute("class") ?? "",
       radius,
       rawRadius,
+      rootFontSize,
     };
   });
 
+  const expected = options.scaleWithRootFont
+    ? expectedRadiusPx * (measurement.rootFontSize / 16)
+    : expectedRadiusPx;
+
   expect(
     measurement.radius,
-    `Expected ${expectedRadiusPx}px corner radius, got ${measurement.rawRadius} on class "${measurement.className}".`,
-  ).toBeCloseTo(expectedRadiusPx, 0);
+    `Expected ${expected}px corner radius, got ${measurement.rawRadius} on class "${measurement.className}".`,
+  ).toBeCloseTo(expected, 0);
 }
 
 export async function expectSmoothCorners(