refactor: 💄 grey navbar border using Quarto css variable (#190)

Author: signekb

_extensions/seedcase-theme/_brand.yml

@@ -16,7 +16,6 @@ color:
     logo-green: "#024639"
     dark-green: "#196440"
     vibrant-green: "#48DC76"
-    dark-grey: "#8B8B8B"
     light-grey: "#F8F9FA"
     code-bg: "#E9ECEFA6"
   primary: dark-green
@@ -45,7 +44,7 @@ typography:
 defaults:
   bootstrap:
     defaults:
-      mermaid-edge-color: var(--brand-dark-grey)
+      mermaid-edge-color: var(--quarto-scss-export-gray-800)
       # Set code background colour variable so all inline code has the same colour
       # including headers with inline code.
       # This colour is the default background colour for inline code.
@@ -56,7 +55,7 @@ defaults:
       }
 
       .navbar {
-          border-bottom: rgba($toc-active-border, 0.3) 1px solid;
+        border-bottom: var(--quarto-scss-export-gray-300) 1px solid;
       }
 
       svg {