add doc

doc/themes/next/source/css/_common/components/components.styl

@@ -0,0 +1,18 @@
+@import "highlight";
+@import "tags";
+
+@import "buttons";
+@import "pagination";
+@import "comments";
+@import (hexo-config('back2top.sidebar') ? "back-to-top-sidebar" : "back-to-top") if (hexo-config('back2top.enable'));
+
+@import "header";
+@import "post";
+@import "sidebar";
+@import "footer";
+@import "third-party";
+
+@import "pages";
+
+@import "rainbow" if hexo-config('safari_rainbow');
+@import "scrollbar" if hexo-config('custom_scrollbar');