top menu dropdown fixes

scss/layout/_layout.scss

@@ -132,10 +132,12 @@ Top nav
 
   & + & {
     top: add($navbar-height, 1px);
+    z-index: $zindex-sticky - 1;
   }
 
   & + & + & {
     top: add($navbar-height * 2, 2px);
+    z-index: $zindex-sticky - 2;
   }
 
   @media print {

scss/layout/_navbar.scss

@@ -28,8 +28,6 @@ Navbar logo
   }
 
   .dropdown-menu {
-    margin-top: 0;
-
     .dropdown,
     .dropright {
       .dropdown-toggle:after {

scss/ui/_dropdowns.scss

@@ -2,6 +2,7 @@
   min-width: 12rem;
   box-shadow: $box-shadow;
   user-select: none;
+  margin: 0;
 
   .icon {
     width: 1em;