Add a section for specific rules for both admin-menu and sub-menu

+ change height for border bottom on selected/hovered menu

app/webpacker/css/admin_v3/components/navigation.scss

@@ -63,14 +63,6 @@ nav.menu {
 #admin-menu {
   box-shadow: 0px 1px 0px rgba(0, 0, 0, 0.05), 0px 2px 2px rgba(0, 0, 0, 0.07);
 
-  ul {
-    justify-content: space-between;
-  }
-
-  li a {
-    font-size: 16px;
-  }
-
   li {
     .dropdown {
       width: 300px;
@@ -94,7 +86,7 @@ nav.menu {
   box-shadow: 0px 1px 0px $light-grey;
 }
 
-// factoized menu item
+// Factorized rules on menu item for admin menu and sub menu
 #admin-menu,
 #sub-menu {
   .container {
@@ -137,6 +129,24 @@ nav.menu {
   }
 }
 
+// Specific rules on menu item for admin menu and sub menu
+#admin-menu {
+  ul {
+    justify-content: space-between;
+    li a {
+      font-size: 16px;
+    }
+  }
+}
+
+#sub-menu {
+  ul li a:hover {
+    &:after {
+      height: 2px;
+    }
+  }
+}
+
 #header figure {
   margin: 0.25em 0;
 }