Organized the description about the border color of toc.

src/client/styles/scss/_layout_growi.scss

@@ -7,7 +7,7 @@
 
   .top-of-table-contents {
     line-height: 1.25;
-    border-bottom: 1px solid transparent;
+    border-bottom: 1px solid $border-color;
 
     .user-list-content {
       direction: rtl;

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

@@ -283,15 +283,3 @@ $table-hover-bg: $bgcolor-table-hover;
     background-color: $bgcolor-tags;
   }
 }
-
-.revision-toc {
-  .top-of-table-contents {
-    border-color: $border-color;
-
-    .grw-seen-user-list {
-      &:before {
-        border-color: $border-color;
-      }
-    }
-  }
-}

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

@@ -14,7 +14,6 @@ $bordercolor-nav-tabs: $gray-300 !default;
 $bordercolor-nav-tabs-hover: $gray-200 $gray-200 $bordercolor-nav-tabs !default;
 $color-nav-tabs-link-active: $gray-600 !default;
 $bordercolor-nav-tabs-active: $bordercolor-nav-tabs $bordercolor-nav-tabs $bgcolor-global !default;
-$bordercolor-toc: $bordercolor-nav-tabs !default;
 $color-seen-user: #549c79 !default;
 
 // override bootstrap variables