Add CSS Custom Properties for caching in head.html and remove migration comment from index.less

Author: lokesh

openlibrary/templates/site/head.html

@@ -31,6 +31,8 @@
     <link href="/static/images/openlibrary-180x180.png" rel="apple-touch-icon" sizes="180x180" />
     <link href="/static/images/openlibrary-192x192.png" rel="icon" sizes="192x192" />
     <link href="/static/images/openlibrary-128x128.png" rel="icon" sizes="128x128" />
+    $# CSS Custom Properties (design tokens) - loaded separately for caching
+    <link href="$static_url('css/less/generated-custom-properties.css')" rel="stylesheet" type="text/css" />
     $ style = 'build/css/page-%s.css'%ctx.get('cssfile', 'user')
     <link href="$static_url(style)" rel="stylesheet" type="text/css" />
 

static/css/less/index.less

@@ -5,6 +5,3 @@
 @import (less) "z-index.less";
 @import (less) "border-radius.less";
 @import (less) "borders.less";
-
-// CSS Custom Properties for native CSS components (migration from Less)
-@import (inline) "generated-custom-properties.css";