chore: add a solid border around the map

Author: jeffabailey

content/en/learn/scaling/markmap_content.md

@@ -1,3 +1,8 @@
+---
+markmap:
+    colorFreezeLevel: 2
+---
+
 # Scaling InnerSource
 
 ## Governance of InnerSource Programs
@@ -57,4 +62,4 @@
 - Engage internal experts
 - Leadership as what a InnerSource project is
 - Projects for Internal Enterprise search
-- Advisory board for InnerSource
+- Advisory board for InnerSource

layouts/shortcodes/markmap.html

@@ -9,6 +9,7 @@
       .markmap > svg {
         width: 100%;
         height: 1000px;
+        border: 1px solid;
       }
 </style>