fix(admin-ui): Fix position of breadcrumb for small screen

admin-ui/src/_variables.scss

@@ -17,3 +17,5 @@ $color-grey-5: #565656;
 $color-grey-6: #313131;
 $color-grey-7: #111111;
 
+// breakpoints
+$breakpoint-small: 768px;

admin-ui/src/app/core/components/app-shell/app-shell.component.scss

@@ -1,3 +1,5 @@
+@import "variables";
+
 .branding {
     min-width: 0;
 }
@@ -5,5 +7,7 @@
     width: 60px;
 }
 vdr-breadcrumb {
-    margin-left: 9rem;
+    @media screen and (min-width: $breakpoint-small){
+        margin-left: 9rem;
+    }
 }