fixed active border on sidebar nav with nav-flat

build/scss/_main-sidebar.scss

@@ -301,6 +301,8 @@
 
         > .nav-item {
           > .nav-link {
+            &,
+            &.active {
               border-color: $sidebar-light-submenu-active-bg;
             }
           }
@@ -308,6 +310,7 @@
       }
     }
   }
+}
 
 [class*='sidebar-dark-'] {
   // Sidebar background color
@@ -425,6 +428,8 @@
 
         > .nav-item {
           > .nav-link {
+            &,
+            &.active {
               border-color: $sidebar-dark-submenu-active-bg;
             }
           }
@@ -432,6 +437,7 @@
       }
     }
   }
+}
 
 // Sidebar variants
 @each $name, $color in $theme-colors {