diff --git a/example/backend/request.js b/example/backend/request.js
index 6d79027..9739bf7 100644
--- a/example/backend/request.js
+++ b/example/backend/request.js
@@ -65,7 +65,7 @@ function fetchParamsFromInit(init) {
   headers.set('origin', HOST_ORIGIN);
   return {
     method: init.method,
-    body: init.body,
+    body: init.body ? new URLSearchParams(init.body) : null,
     headers,
     redirect: 'error',
     credentials: 'omit',
diff --git a/example/frontend/tester/index.js b/example/frontend/tester/index.js
index 35ca697..f9bd548 100644
--- a/example/frontend/tester/index.js
+++ b/example/frontend/tester/index.js
@@ -25,6 +25,7 @@ window.ampContainerConfig = Object.assign(
     imageProxyURL: process.env.CONFIG_IMAGE_PROXY_URL,
     xhrProxyURL: process.env.CONFIG_XHR_PROXY_URL,
     templateProxyURL: process.env.CONFIG_TEMPLATE_PROXY_URL,
+    transformTemplateProxyOutput: true,
     linkRedirectURL: process.env.CONFIG_LINK_REDIRECT_URL,
     loadTimeout: 3000,
   },
diff --git a/example/package.json b/example/package.json
index 4d6c200..63f1ab3 100644
--- a/example/package.json
+++ b/example/package.json
@@ -9,7 +9,7 @@
     "parcel-bundler": "^1.12.4"
   },
   "scripts": {
-    "test": "jest --forceExit"
+    "test": "jest --forceExit --runInBand"
   },
   "alias": {
     "@ampproject/email-viewer": ".."
diff --git a/src/framecontainer/rendering-modules/ViewerRenderProxy.ts b/src/framecontainer/rendering-modules/ViewerRenderProxy.ts
index 601fae6..f99ab7a 100644
--- a/src/framecontainer/rendering-modules/ViewerRenderProxy.ts
+++ b/src/framecontainer/rendering-modules/ViewerRenderProxy.ts
@@ -4,7 +4,11 @@ import { parseHTMLFragment, serializeHTML, postJSON } from '../../util';
 import { transformingModules } from '../../preprocessing/preprocessing-modules/index';
 import { Config } from '../../config';
 
-const TEMPLATE_TRANSFORMING_MODULES = ['HyperlinkRewrite', 'ImageURLRewrite'];
+const TEMPLATE_TRANSFORMING_MODULES = [
+  'CSS',
+  'HyperlinkRewrite',
+  'ImageURLRewrite',
+];
 
 /**
  * Proxies XHR requests that include mustache template rendering coming from the
diff --git a/src/preprocessing/preprocessing-modules/CSS/whitelist.ts b/src/preprocessing/preprocessing-modules/CSS/whitelist.ts
index 5171776..a1b24e8 100644
--- a/src/preprocessing/preprocessing-modules/CSS/whitelist.ts
+++ b/src/preprocessing/preprocessing-modules/CSS/whitelist.ts
@@ -61,8 +61,10 @@ export const ALLOWED_PROPERTIES_WITH_URL = new Set([
 ]);
 
 export const ALLOWED_PROPERTIES = new Set([
+  '-moz-appearance',
   '-webkit-appearance',
   '-webkit-tap-highlight-color',
+  'align-content',
   'align-items',
   'align-self',
   'appearance',
@@ -158,6 +160,7 @@ export const ALLOWED_PROPERTIES = new Set([
   'font-variant-numeric',
   'font-variation-settings',
   'font-weight',
+  'gap',
   'grid',
   'grid-area',
   'grid-auto-columns',
@@ -231,6 +234,7 @@ export const ALLOWED_PROPERTIES = new Set([
   'resize',
   'richness',
   'right',
+  'row-gap',
   'speak',
   'speak-header',
   'speak-numeral',