theme_var() twig function now checks page header var first

CHANGELOG.md

@@ -13,6 +13,7 @@
 1. [](#improved)
     * Vendor library updated to latest  
     * Improved `Session` initialization
+    * Added ability to set a `theme_var()` option in page frontmatter
 1. [](#bugfix) 
     * Fixed issue with image alt tag always getting empted out unless set in markdown
     * Fixed issue with remote PHP version determination for Grav updates [#1883](https://github.com/getgrav/grav/issues/1883)

system/src/Grav/Common/Twig/TwigExtension.php

@@ -1129,7 +1129,9 @@ class TwigExtension extends \Twig_Extension implements \Twig_Extension_GlobalsIn
      */
     public function themeVarFunc($var, $default = null)
     {
-        return $this->config->get('theme.' . $var, $default);
+        $header = $this->grav['page']->header();
+        $header_classes = isset($header->$var) ? $header->$var : null;
+        return $header_classes ?: $this->config->get('theme.' . $var, $default);
     }
 
     /**