Switch to SCSS syntax to resolve abiguous syntax issues in SASS

src/_hidden.scss

@@ -0,0 +1,9 @@
+/**
+ * 1. Address `[hidden]` styling not present in IE 8/9/10 and hide the
+ *    `template` element in IE 8/9/10/11, Safari, and Firefox < 22
+ *    (from normalize.css).
+ */
+[hidden],
+template {
+  display: none; /* 1 */
+}