Update intro-header.html

Author: TwperBody

_includes/intro-header.html

@@ -13,8 +13,8 @@
 
     {% if page.header-mask %}
     header.intro-header .header-mask{
-        width: 120%;
-        height: 120%;
+        width: 80%;
+        height: 80%;
         position: absolute;
         background: rgba(0,0,0, {{ page.header-mask }});
     }