fix(cssnano-preset): disable z-index minification (#7593)

* fix(cssnano-preset): disable z-index minification

* add z-index tests link to pages tests

* revert change to docs

packages/docusaurus-cssnano-preset/src/index.ts

@@ -13,6 +13,8 @@ const preset: typeof advancedBasePreset = function preset(opts) {
   const advancedPreset = advancedBasePreset({
     autoprefixer: {add: false},
     discardComments: {removeAll: true},
+    /* cSpell:ignore zindex */
+    zindex: false,
     ...opts,
   });
 

website/_dogfooding/_pages tests/index.md

@@ -28,3 +28,4 @@ import Readme from "../README.md"
 - [General Markdown tests](/tests/pages/markdownPageTests)
 - [TOC tests](/tests/pages/page-toc-tests)
 - [Tabs tests](/tests/pages/tabs-tests)
+- [z-index tests](/tests/pages/z-index-tests)

website/_dogfooding/_pages tests/z-index-tests.tsx

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import React from 'react';
+import Layout from '@theme/Layout';
+
+export default function zIndexTest(): JSX.Element {
+  return (
+    <Layout>
+      <p id="z-index-test">This should have a z-index of 100</p>
+    </Layout>
+  );
+}

website/_dogfooding/dogfooding.css

@@ -20,3 +20,7 @@ html.plugin-blog.plugin-id-blog-tests .navbar {
 html.plugin-pages.plugin-id-pages-tests .navbar {
   border-bottom: solid thin yellow;
 }
+
+#z-index-test {
+  z-index: 100;
+}