diff --git a/.github/workflows/browser-smoke.yml b/.github/workflows/browser-smoke.yml
new file mode 100644
index 0000000..c3d6a18
--- /dev/null
+++ b/.github/workflows/browser-smoke.yml
@@ -0,0 +1,40 @@
+name: Browser smoke
+
+on:
+  pull_request:
+    paths:
+      - "src/**"
+      - "tests/browserSmoke.cjs"
+      - "package.json"
+      - "package-lock.json"
+      - "vite.config.ts"
+      - ".github/workflows/browser-smoke.yml"
+  push:
+    branches: [main]
+    paths:
+      - "src/**"
+      - "tests/browserSmoke.cjs"
+      - "package.json"
+      - "package-lock.json"
+      - "vite.config.ts"
+      - ".github/workflows/browser-smoke.yml"
+
+permissions:
+  contents: read
+
+jobs:
+  browser-smoke:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+          cache: npm
+      - run: npm ci
+      - name: Install pinned browser test tooling
+        run: |
+          npm install --no-save --package-lock=false playwright@1.56.1
+          npx playwright install --with-deps chromium
+      - run: node tests/browserSmoke.cjs
diff --git a/src/utils/yamlGenerator.ts b/src/utils/yamlGenerator.ts
index 58cb5f3..ce8d86e 100644
--- a/src/utils/yamlGenerator.ts
+++ b/src/utils/yamlGenerator.ts
@@ -1438,7 +1438,7 @@ export const generateYaml = (
         if (field.styles) {
           field.styles.split('\n').forEach(line => {
             if (line.trim()) {
-              yaml += `      - ${line.trim()}\n`;
+              yaml += `      - ${formatStyleForYaml(line.trim())}\n`;
             }
           });
         }
diff --git a/src/utils/yamlImporter.ts b/src/utils/yamlImporter.ts
index b1bd2fb..ee3f999 100644
--- a/src/utils/yamlImporter.ts
+++ b/src/utils/yamlImporter.ts
@@ -693,7 +693,13 @@ function parseStyles(styles: any, config: Partial<ButtonConfig>): void {
       for (const field of config.customFields) {
         if (styles.custom_fields[field.name] && Array.isArray(styles.custom_fields[field.name])) {
           field.styles = styles.custom_fields[field.name]
-            .filter((s: any) => typeof s === 'string')
+            .flatMap((style: any) => {
+              if (typeof style === 'string') return [style];
+              if (style && typeof style === 'object' && !Array.isArray(style)) {
+                return Object.entries(style).map(([property, value]) => `${property}: ${String(value ?? '')}`);
+              }
+              return [];
+            })
             .join('\n');
         }
       }
diff --git a/tests/browserSmoke.cjs b/tests/browserSmoke.cjs
new file mode 100644
index 0000000..6236d36
--- /dev/null
+++ b/tests/browserSmoke.cjs
@@ -0,0 +1,61 @@
+'use strict';
+
+const assert = require('node:assert/strict');
+const { spawn } = require('node:child_process');
+const { chromium } = require('playwright');
+
+const address = 'http://127.0.0.1:4173/button_builder/';
+const server = spawn(process.execPath, ['node_modules/vite/bin/vite.js', '--host', '127.0.0.1', '--port', '4173', '--strictPort'], {
+  stdio: ['ignore', 'pipe', 'pipe'],
+});
+let logs = '';
+server.stdout.on('data', chunk => { logs += chunk.toString(); });
+server.stderr.on('data', chunk => { logs += chunk.toString(); });
+
+const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
+async function ready() {
+  for (let i = 0; i < 80; i++) {
+    if (server.exitCode !== null) throw new Error('Vite exited early: ' + logs);
+    try {
+      const response = await fetch(address, { signal: AbortSignal.timeout(1000) });
+      if (response.ok) return;
+    } catch {}
+    await sleep(250);
+  }
+  throw new Error('Vite did not become ready: ' + logs);
+}
+(async () => {
+  let browser;
+  try {
+    await ready();
+    browser = await chromium.launch({ headless: true });
+    const page = await browser.newPage({ viewport: { width: 1440, height: 900 } });
+    const errors = [];
+    page.on('pageerror', error => errors.push(error.message));
+    await page.goto(address, { waitUntil: 'domcontentloaded' });
+    await page.getByRole('heading', { name: 'Button Card Builder' }).waitFor({ timeout: 20000 });
+    await page.locator('.preview-workbench .preview-toolbar').first().waitFor({ timeout: 15000 });
+    assert.equal(errors.length, 0, 'Uncaught browser exceptions: ' + errors.join('; '));
+    assert.equal(await page.getByText('Button Builder failed to load:', { exact: false }).count(), 0);
+    // On a fresh browser profile, Button Builder first asks about theme defaults.
+    const themeDialog = page.getByRole('heading', { name: 'Theme options' });
+    if (await themeDialog.isVisible()) {
+      await page.getByRole('button', { name: 'Start with no theme' }).click();
+    }
+    // The standalone preview can show the first-run requirements dialog.
+    // Dismiss it through the same Continue control a user would press.
+    const requirements = page.getByRole('heading', { name: 'Home Assistant Requirements Check' });
+    await requirements.waitFor({ state: 'visible', timeout: 5000 }).catch(error => {
+      if (error.name !== 'TimeoutError') throw error;
+    });
+    if (await requirements.isVisible()) {
+      await page.getByRole('button', { name: 'Continue' }).click();
+    }
+    await page.getByRole('button', { name: 'Switch to light mode' }).click();
+    assert.equal(await page.locator('html.bb-light').count(), 1, 'Theme toggle must apply light mode');
+    console.log('Browser smoke passed: editor, preview, no runtime crash, theme toggle.');
+  } finally {
+    if (browser) await browser.close();
+    server.kill('SIGTERM');
+  }
+})().catch(error => { console.error(error); process.exitCode = 1; });
diff --git a/tests/yamlRoundTrip.test.cjs b/tests/yamlRoundTrip.test.cjs
index 5bb7b58..8ec0b6a 100644
--- a/tests/yamlRoundTrip.test.cjs
+++ b/tests/yamlRoundTrip.test.cjs
@@ -86,3 +86,52 @@ test('retains JavaScript action templates', () => {
 test('rejects invalid YAML instead of fabricating an empty configuration', () => {
   assert.throws(() => parseButtonCardYaml('entity: [unterminated'), /./);
 });
+
+test('preserves template custom fields and their style declarations', () => {
+  const value = '[[[ return entity.state === "on" ? "Active" : "Idle"; ]]]';
+  const { imported, parsed } = roundTrip({
+    type: 'custom:button-card',
+    entity: 'switch.desk',
+    custom_fields: { status: value },
+    styles: { custom_fields: { status: ['color: #33cc66', 'font-weight: bold'] } },
+  });
+  assert.equal(imported.customFields[0].type, 'template');
+  assert.equal(parsed.custom_fields.status.trim(), value);
+  assert.deepEqual(parsed.styles.custom_fields.status, [{ color: '#33cc66' }, { 'font-weight': 'bold' }]);
+});
+
+test('retains a regex state override with its icon and label', () => {
+  const { imported, parsed } = roundTrip({
+    type: 'custom:button-card',
+    entity: 'sensor.machine',
+    state: [{ operator: 'regex', value: '^error', icon: 'mdi:alert', label: 'Needs attention' }],
+  });
+  assert.equal(imported.stateStyles.length, 1);
+  const state = parsed.state.find(x => x.operator === 'regex');
+  assert.ok(state);
+  assert.equal(state.value, '^error');
+  assert.equal(state.icon, 'mdi:alert');
+  assert.equal(state.label, 'Needs attention');
+});
+
+test('preserves the default-state fallback after import and export', () => {
+  const { parsed } = roundTrip({
+    type: 'custom:button-card',
+    entity: 'sensor.machine',
+    state: [{ operator: 'default', name: 'Normal operation', icon: 'mdi:check' }],
+  });
+  const fallback = parsed.state.find(x => x.operator === 'default');
+  assert.ok(fallback);
+  assert.equal(fallback.name, 'Normal operation');
+  assert.equal(fallback.icon, 'mdi:check');
+});
+
+test('preserves custom-field text with YAML-special characters', () => {
+  const value = 'Floor 2: "Office" #1';
+  const { parsed } = roundTrip({
+    type: 'custom:button-card',
+    entity: 'switch.office',
+    custom_fields: { location: value },
+  });
+  assert.equal(parsed.custom_fields.location, value);
+});