adjust header styles

src/client/styles/scss/theme/_apply-colors-dark.scss

@@ -139,6 +139,12 @@ header.affix {
 /*
  * GROWI subnavigation
  */
+.admin-page {
+  .grw-header {
+    background-color: rgba(darken($bgcolor-global, 90%), 0.9);
+  }
+}
+
 .grw-subnavbar-sticky {
   background-color: rgba(darken($bgcolor-global, 90%), 0.9);
   box-shadow: 0 3px 2px -2px darken($bgcolor-global, 5%);

src/client/styles/scss/theme/_apply-colors-light.scss

@@ -35,6 +35,12 @@ header.affix {
 /*
  * GROWI subnavigation
  */
+.admin-page {
+  .grw-header {
+    background-color: rgba(darken($bgcolor-global, 6%), 0.9);
+  }
+}
+
 .grw-subnavbar-sticky {
   background-color: rgba(darken($bgcolor-global, 6%), 0.9);
   box-shadow: 0 3px 2px -2px darken($bgcolor-global, 40%);

src/client/styles/scss/theme/_apply-colors.scss

@@ -85,12 +85,6 @@ $link-hover-color: $color-link-hover;
   }
 }
 
-.admin-page {
-  .grw-header {
-    background: darken($bgcolor-global, 2%);
-  }
-}
-
 .grw-sidebar {
   .grw-logo {
     background-color: darken($bgcolor-navbar, 10%);