diff --git a/e2e/tests/import-error.test.ts b/e2e/tests/import-error.test.ts
new file mode 100644
index 0000000..ac64026
--- /dev/null
+++ b/e2e/tests/import-error.test.ts
@@ -0,0 +1,59 @@
+import { test, expect } from '../fixtures/extension.js';
+import { openPanelPage } from '../helpers/panel-page.js';
+
+test.describe('import error handling', () => {
+  test('submitting invalid JSON shows error banner', async ({ extensionContext, extensionId }) => {
+    const panelPage = await extensionContext.newPage();
+    await openPanelPage(panelPage, extensionId);
+
+    // Open import paste area
+    const importBtn = panelPage.locator('.tb-btn', { hasText: 'Import' });
+    await importBtn.click();
+
+    const pasteArea = panelPage.locator('.import-paste-textarea');
+    await expect(pasteArea).toBeVisible();
+
+    // Paste invalid JSON
+    await pasteArea.fill('not valid json {{{');
+    const submitBtn = panelPage.locator('.import-paste .tb-btn', { hasText: 'Import' });
+    await submitBtn.click();
+
+    // Error banner should appear
+    const errBanner = panelPage.locator('.err-banner');
+    await expect(errBanner).toBeVisible({ timeout: 3000 });
+
+    // Panel should remain functional
+    await expect(panelPage.locator('.toolbar')).toBeVisible();
+
+    await panelPage.close();
+  });
+
+  test('submitting valid JSON with wrong schema shows error banner', async ({
+    extensionContext,
+    extensionId,
+  }) => {
+    const panelPage = await extensionContext.newPage();
+    await openPanelPage(panelPage, extensionId);
+
+    // Open import paste area
+    const importBtn = panelPage.locator('.tb-btn', { hasText: 'Import' });
+    await importBtn.click();
+
+    const pasteArea = panelPage.locator('.import-paste-textarea');
+    await expect(pasteArea).toBeVisible();
+
+    // Paste valid JSON but wrong schema (missing required fields)
+    await pasteArea.fill(JSON.stringify({ version: 999, flow: {} }));
+    const submitBtn = panelPage.locator('.import-paste .tb-btn', { hasText: 'Import' });
+    await submitBtn.click();
+
+    // Error banner should appear
+    const errBanner = panelPage.locator('.err-banner');
+    await expect(errBanner).toBeVisible({ timeout: 3000 });
+
+    // Panel should remain functional
+    await expect(panelPage.locator('.toolbar')).toBeVisible();
+
+    await panelPage.close();
+  });
+});
diff --git a/e2e/tests/payload-tab.test.ts b/e2e/tests/payload-tab.test.ts
new file mode 100644
index 0000000..66c6753
--- /dev/null
+++ b/e2e/tests/payload-tab.test.ts
@@ -0,0 +1,69 @@
+import { test, expect } from '../fixtures/extension.js';
+import { openPanelPage } from '../helpers/panel-page.js';
+import {
+  injectDiscovery,
+  injectTokenRequest,
+  reloadAndWaitForEvents,
+} from '../helpers/inject-events.js';
+
+test.describe('payload tab', () => {
+  test('Payload tab appears for network events with request/response body', async ({
+    extensionContext,
+    extensionId,
+    mockServer,
+  }) => {
+    const panelPage = await extensionContext.newPage();
+    await openPanelPage(panelPage, extensionId);
+
+    // Inject discovery + token request (token has postData and JSON response body)
+    await injectDiscovery(panelPage, mockServer.baseUrl);
+    await injectTokenRequest(panelPage, mockServer.baseUrl);
+    await reloadAndWaitForEvents(panelPage, 2);
+
+    // Select the token event (second row, after discovery)
+    await panelPage.locator('.tl-row').nth(1).click();
+
+    // Payload tab should be visible (event has requestBody + responseBody)
+    const payloadTab = panelPage.locator('.tab-btn', { hasText: 'Payload' });
+    await expect(payloadTab).toBeVisible({ timeout: 3000 });
+
+    // Click the Payload tab
+    await payloadTab.click();
+    await expect(payloadTab).toHaveClass(/active/);
+
+    // Should show payload sections
+    await expect(panelPage.locator('.payload-section').first()).toBeVisible();
+    await expect(panelPage.locator('.sect-hdr', { hasText: 'Request Body' })).toBeVisible();
+    await expect(panelPage.locator('.sect-hdr', { hasText: 'Response Body' })).toBeVisible();
+
+    await panelPage.close();
+  });
+
+  test('Payload tab for discovery events shows only Response Body section', async ({
+    extensionContext,
+    extensionId,
+    mockServer,
+  }) => {
+    const panelPage = await extensionContext.newPage();
+    await openPanelPage(panelPage, extensionId);
+
+    // Discovery is a GET request with no postData — only has responseBody
+    await injectDiscovery(panelPage, mockServer.baseUrl);
+    await injectTokenRequest(panelPage, mockServer.baseUrl);
+    await reloadAndWaitForEvents(panelPage, 2);
+
+    // Select the discovery event (first row) — it's a GET with no postData
+    await panelPage.locator('.tl-row').first().click();
+
+    // Discovery has responseBody (the OIDC config JSON), so Payload tab
+    // should appear. But it has no requestBody, so only Response Body shows.
+    const payloadTab = panelPage.locator('.tab-btn', { hasText: 'Payload' });
+    await expect(payloadTab).toBeVisible({ timeout: 3000 });
+    await payloadTab.click();
+    await expect(payloadTab).toHaveClass(/active/);
+    await expect(panelPage.locator('.sect-hdr', { hasText: 'Response Body' })).toBeVisible();
+    await expect(panelPage.locator('.sect-hdr', { hasText: 'Request Body' })).not.toBeVisible();
+
+    await panelPage.close();
+  });
+});
diff --git a/e2e/tests/theme-toggle.test.ts b/e2e/tests/theme-toggle.test.ts
new file mode 100644
index 0000000..1138bcc
--- /dev/null
+++ b/e2e/tests/theme-toggle.test.ts
@@ -0,0 +1,122 @@
+import { test, expect } from '../fixtures/extension.js';
+import { openPanelPage } from '../helpers/panel-page.js';
+
+test.describe('theme toggle', () => {
+  test('theme toggle button is visible in toolbar', async ({ extensionContext, extensionId }) => {
+    const panelPage = await extensionContext.newPage();
+    await openPanelPage(panelPage, extensionId);
+
+    // The theme toggle is appended by JS after Elm renders the toolbar
+    const toggleBtn = panelPage.locator('.theme-toggle');
+    await expect(toggleBtn).toBeVisible({ timeout: 3000 });
+
+    await panelPage.close();
+  });
+
+  test('clicking toggle switches to light mode and back', async ({
+    extensionContext,
+    extensionId,
+  }) => {
+    const panelPage = await extensionContext.newPage();
+    await openPanelPage(panelPage, extensionId);
+
+    const toggleBtn = panelPage.locator('.theme-toggle');
+    await expect(toggleBtn).toBeVisible({ timeout: 3000 });
+
+    // Get initial theme state
+    const initialTheme = await panelPage.evaluate(() =>
+      document.documentElement.getAttribute('data-theme'),
+    );
+
+    // Click to switch theme
+    await toggleBtn.click();
+    const afterFirstClick = await panelPage.evaluate(() =>
+      document.documentElement.getAttribute('data-theme'),
+    );
+
+    if (initialTheme === null) {
+      expect(afterFirstClick).toBe('light');
+    } else {
+      expect(afterFirstClick).toBeNull();
+    }
+
+    // Click again to toggle back
+    await toggleBtn.click();
+    const afterSecondClick = await panelPage.evaluate(() =>
+      document.documentElement.getAttribute('data-theme'),
+    );
+    expect(afterSecondClick).toBe(initialTheme);
+
+    await panelPage.close();
+  });
+
+  test('theme preference persists across page reloads', async ({
+    extensionContext,
+    extensionId,
+  }) => {
+    const panelPage = await extensionContext.newPage();
+    await openPanelPage(panelPage, extensionId);
+
+    const toggleBtn = panelPage.locator('.theme-toggle');
+    await expect(toggleBtn).toBeVisible({ timeout: 3000 });
+
+    // Get initial state
+    const initialTheme = await panelPage.evaluate(() =>
+      document.documentElement.getAttribute('data-theme'),
+    );
+
+    // Toggle the theme
+    await toggleBtn.click();
+    const newTheme = await panelPage.evaluate(() =>
+      document.documentElement.getAttribute('data-theme'),
+    );
+    expect(newTheme).not.toBe(initialTheme);
+
+    // Verify localStorage was updated
+    const storedTheme = await panelPage.evaluate(() => localStorage.getItem('wolfcola:theme'));
+    expect(storedTheme).toBe(newTheme === 'light' ? 'light' : 'dark');
+
+    // Reload and verify theme persists
+    await panelPage.reload();
+    await panelPage.waitForSelector('.toolbar', { state: 'visible' });
+
+    const themeAfterReload = await panelPage.evaluate(() =>
+      document.documentElement.getAttribute('data-theme'),
+    );
+    expect(themeAfterReload).toBe(newTheme);
+
+    await panelPage.close();
+  });
+
+  test('toggle button survives Elm re-render', async ({ extensionContext, extensionId }) => {
+    const panelPage = await extensionContext.newPage();
+    await openPanelPage(panelPage, extensionId);
+
+    await expect(panelPage.locator('.theme-toggle')).toBeVisible({ timeout: 3000 });
+
+    // Trigger an Elm re-render by injecting an SDK event
+    await panelPage.evaluate(() => {
+      chrome.runtime.sendMessage({
+        type: 'SDK_EVENT',
+        payload: {
+          type: 'sdk:node-change',
+          id: `theme-test-${Date.now()}`,
+          flowId: 'theme-flow',
+          timestamp: Date.now(),
+          source: 'sdk',
+          causedBy: null,
+          data: { _tag: 'sdk', nodeStatus: 'continue' },
+          flags: { isCors: false, isError: false, isAuthRelated: true },
+        },
+      });
+    });
+
+    // Wait for the event to appear (forces Elm re-render)
+    await panelPage.waitForSelector('.tl-row', { state: 'visible', timeout: 5000 });
+
+    // Toggle should still be there after Elm re-rendered
+    await expect(panelPage.locator('.theme-toggle')).toBeVisible({ timeout: 3000 });
+
+    await panelPage.close();
+  });
+});
diff --git a/packages/devtools-extension/src/panel/panel.ts b/packages/devtools-extension/src/panel/panel.ts
index 4ef8bee..4c4c9a0 100644
--- a/packages/devtools-extension/src/panel/panel.ts
+++ b/packages/devtools-extension/src/panel/panel.ts
@@ -129,6 +129,13 @@ function initThemeToggle() {
     }
   });
   observer.observe(document.body, { childList: true, subtree: true });
+
+  // Eagerly append if the toolbar already exists (Elm.Main.init runs before
+  // initThemeToggle, so the initial render mutation has already fired).
+  const toolbar = document.querySelector('.toolbar');
+  if (toolbar) {
+    toolbar.appendChild(btn);
+  }
 }
 
 // ── App init ──────────────────────────────────────────────────────────────────
diff --git a/packages/devtools-ui/src/panel.css b/packages/devtools-ui/src/panel.css
index 2aa31af..023dc29 100644
--- a/packages/devtools-ui/src/panel.css
+++ b/packages/devtools-ui/src/panel.css
@@ -1133,7 +1133,7 @@ details[open] > .jwt-summary::before {
   top: 0;
   left: var(--graph-w);
   width: 5px;
-  height: 100%;
+  height: calc(100% - var(--insp-h, 220px));
   cursor: col-resize;
   transform: translateX(-2px);
 }