fix purgecss remove code pre blocquote tags

resources/sass/pages/memos.scss

@@ -31,9 +31,7 @@
 
     pre,
     code {
-        @apply text-white p-1;
+        @apply bg-gray-700 text-white p-1;
-        background-color: #4A5568;
-        //color: #ffffff;
     }
 
     pre {

webpack.mix.js

@@ -10,4 +10,4 @@ mix.js('resources/js/app.js', 'public/js')
         processCssUrls: false,
         postCss: [ tailwindcss('./tailwind.config.js') ],
     })
-    .purgeCss();
+    .purgeCss({whitelistPatterns: [/-active$/, /-enter$/, /-leave-to$/, /show$/, /code$/, /pre$/, /blockquote$/]});