Put in workarounds for the webpack for the html manager test suite.

Author: jasongrout

jupyter-widgets-htmlmanager/test/webpack.conf.js

@@ -1,4 +1,5 @@
 var path = require('path');
+var postcss = require('postcss');
 
 module.exports = {
     entry: './test/build/index.js',
@@ -17,10 +18,22 @@ module.exports = {
             { test: /\.json$/, loader: 'json-loader' },
         ],
     },
-    postcss: function () {
+    postcss: () => {
         return [
-            require('postcss-import'),
-            require('postcss-cssnext')
+            postcss.plugin('delete-tilde', () => {
+                return function (css) {
+                    css.walkAtRules('import', (rule) => {
+                        rule.params = rule.params.replace('~', '');
+                    });
+                };
+            }),
+            postcss.plugin('prepend', () => {
+                return (css) => {
+                    css.prepend(`@import '@jupyter-widgets/controls/css/labvariables.css';`)
+                }
+            }),
+            require('postcss-import')(),
+            require('postcss-cssnext')()
         ];
     }
 }