[ticket/12719] Add normalize & base

phpbb3-12719

phpBB/styles/prosilver/theme/stylesheet.css

@@ -7,6 +7,9 @@
     --------------------------------------------------------------
 */
 
+@import url("normalize.css");
+@import url("base.css");
+@import url("utilities.css");
 @import url("common.css");
 @import url("links.css");
 @import url("content.css");