Checkbox: support different shape

postcss.config.js

@@ -1,11 +1,12 @@
 module.exports = {
   plugins: [
-    require("postcss-easy-import")({
+    require('postcss-easy-import')({
       extensions: ['pcss', 'css']
     }),
-    require("precss")(),
-    require("autoprefixer")({
-      browsers: ["Android >= 4.0", "iOS >= 7"]
+    require('precss')(),
+    require('postcss-calc')(),
+    require('autoprefixer')({
+      browsers: ['Android >= 4.0', 'iOS >= 7']
     })
   ]
 };