Fix popover shadow in app menu

Make sure the app menu popover shadow does overlay the active indicator

Signed-off-by: Julius Härtl <jus@bitgrid.net>

core/css/header.scss

@@ -498,6 +498,7 @@ nav {
 		transform: translateX(-50%);
 		padding: 4px 10px;
 		filter: drop-shadow(0 1px 10px $color-box-shadow);
+		z-index: 100;
 	}
 
 	li:hover span {
@@ -518,7 +519,6 @@ nav {
 		transform: translateX(-50%);
 		left: 50%;
 		bottom: 0;
-		z-index: 100;
 		display: none;
 	}
 	li a.active:before,
@@ -526,6 +526,13 @@ nav {
 	li:hover a.active:before {
 		display: block;
 	}
+	li a.active:before {
+		z-index: 99;
+	}
+	li:hover a:before,
+	li a.active:hover:before {
+		z-index: 101;
+	}
 	&.menu-open li:hover a:before,
 	&.menu-open li a.active:before,
 	&.menu-open li:hover span {