diff --git a/workout-tracker/e2e/rest-timer-visibility.spec.ts b/workout-tracker/e2e/rest-timer-visibility.spec.ts
new file mode 100644
index 0000000..f483934
--- /dev/null
+++ b/workout-tracker/e2e/rest-timer-visibility.spec.ts
@@ -0,0 +1,89 @@
+import { test, expect } from '@playwright/test';
+
+/**
+ * TDD: Rest timer should be the most prominent element during rest.
+ * It should overlay the header so it cannot be occluded.
+ */
+test.describe('Rest Timer Visibility', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/');
+    await page.waitForSelector('#app');
+    await page.click('#start-workout-btn');
+    await page.waitForSelector('.workout-screen');
+  });
+
+  test('rest timer covers the header area when active', async ({ page }) => {
+    // Complete first set to trigger rest timer
+    await page.click('[data-testid="done-set-btn"]');
+
+    const timer = page.locator('#rest-timer');
+    await expect(timer).toBeVisible();
+
+    // Timer should be at the very top of the viewport (covering the header)
+    const timerBox = await timer.boundingBox();
+    expect(timerBox).not.toBeNull();
+    expect(timerBox!.y).toBeLessThanOrEqual(10); // At or near top of viewport
+  });
+
+  test('rest timer has a large, prominent countdown display', async ({ page }) => {
+    await page.click('[data-testid="done-set-btn"]');
+
+    const timerValue = page.locator('#timer-value');
+    await expect(timerValue).toBeVisible();
+
+    // Timer value font size should be large (at least 2.5rem = 40px)
+    const fontSize = await timerValue.evaluate((el) => {
+      return parseFloat(getComputedStyle(el).fontSize);
+    });
+    expect(fontSize).toBeGreaterThanOrEqual(40);
+  });
+
+  test('rest timer has higher z-index than the header', async ({ page }) => {
+    await page.click('[data-testid="done-set-btn"]');
+
+    const timerZ = await page.locator('#rest-timer').evaluate((el) => {
+      return parseInt(getComputedStyle(el).zIndex || '0', 10);
+    });
+    const headerZ = await page.locator('.app-header').evaluate((el) => {
+      return parseInt(getComputedStyle(el).zIndex || '0', 10);
+    });
+
+    expect(timerZ).toBeGreaterThan(headerZ);
+  });
+
+  test('rest timer spans the full width of the app', async ({ page }) => {
+    await page.click('[data-testid="done-set-btn"]');
+
+    const timer = page.locator('#rest-timer');
+    await expect(timer).toBeVisible();
+
+    const timerBox = await timer.boundingBox();
+    const appBox = await page.locator('#app').boundingBox();
+
+    expect(timerBox).not.toBeNull();
+    expect(appBox).not.toBeNull();
+    // Timer should be nearly full-width (within a few pixels for border/padding)
+    expect(timerBox!.width).toBeGreaterThanOrEqual(appBox!.width - 2);
+  });
+
+  test('skip button remains accessible on the rest timer overlay', async ({ page }) => {
+    await page.click('[data-testid="done-set-btn"]');
+
+    const skipBtn = page.locator('#skip-timer-btn');
+    await expect(skipBtn).toBeVisible();
+    await expect(skipBtn).toBeInViewport();
+
+    // Clicking skip still works
+    await skipBtn.click();
+    await expect(page.locator('#rest-timer')).toBeHidden();
+  });
+
+  test('rest timer visual snapshot', async ({ page }) => {
+    await page.click('[data-testid="done-set-btn"]');
+    await expect(page.locator('#rest-timer')).toBeVisible();
+
+    await expect(page).toHaveScreenshot('rest-timer-overlay.png', {
+      maxDiffPixelRatio: 0.05,
+    });
+  });
+});
diff --git a/workout-tracker/e2e/rest-timer-visibility.spec.ts-snapshots/rest-timer-overlay-chromium-linux.png b/workout-tracker/e2e/rest-timer-visibility.spec.ts-snapshots/rest-timer-overlay-chromium-linux.png
new file mode 100644
index 0000000..b2a8a5c
Binary files /dev/null and b/workout-tracker/e2e/rest-timer-visibility.spec.ts-snapshots/rest-timer-overlay-chromium-linux.png differ
diff --git a/workout-tracker/e2e/rest-timer-visibility.spec.ts-snapshots/rest-timer-overlay-mobile-chrome-linux.png b/workout-tracker/e2e/rest-timer-visibility.spec.ts-snapshots/rest-timer-overlay-mobile-chrome-linux.png
new file mode 100644
index 0000000..61a0008
Binary files /dev/null and b/workout-tracker/e2e/rest-timer-visibility.spec.ts-snapshots/rest-timer-overlay-mobile-chrome-linux.png differ
diff --git a/workout-tracker/src/style.css b/workout-tracker/src/style.css
index 09514fb..6832968 100644
--- a/workout-tracker/src/style.css
+++ b/workout-tracker/src/style.css
@@ -266,15 +266,18 @@ body {
 .rest-timer {
   background: var(--color-accent);
   color: #fff;
-  border-radius: var(--radius);
-  padding: 16px;
+  padding: 20px 16px;
   display: flex;
   align-items: center;
   gap: 12px;
-  margin-bottom: 16px;
-  position: sticky;
-  top: 60px;
-  z-index: 9;
+  position: fixed;
+  top: 0;
+  left: 50%;
+  transform: translateX(-50%);
+  width: 100%;
+  max-width: 600px;
+  z-index: 15;
+  border-radius: 0 0 var(--radius) var(--radius);
 }
 
 .rest-timer.hidden {
@@ -282,13 +285,14 @@ body {
 }
 
 .timer-label {
-  font-size: 0.85rem;
-  font-weight: 600;
+  font-size: 0.9rem;
+  font-weight: 700;
   text-transform: uppercase;
+  letter-spacing: 0.05em;
 }
 
 .timer-value {
-  font-size: 1.8rem;
+  font-size: 3rem;
   font-weight: 700;
   font-variant-numeric: tabular-nums;
   flex: 1;