XWIKI-23413: Separators in navigation tree dropdown (#4403)

* Reverted generic changes from XWIKI-22485 to make them more specific and added them in the Livedata CSS.

(cherry picked from commit 4a209c2)

Author: Sereza7

xwiki-platform-core/xwiki-platform-bootstrap/src/main/less/dropdowns.less

@@ -59,15 +59,6 @@
     .nav-divider(@dropdown-divider-bg);
   }
 
-  // Dividers within the dropdown with an improved semantic representation
-  li:has(> ul) + li:has(> ul) {
-    padding-top: ((@line-height-computed / 2) - 1);
-    border-top: solid 1px @dropdown-divider-bg;
-  }
-  li:has(> ul):has(+ li > ul) {
-    margin-bottom: ((@line-height-computed / 2) - 1);
-  }
-
   // Links within the dropdown menu and submenus
   /* stylelint-disable selector-max-compound-selectors */
   > li > a,

xwiki-platform-core/xwiki-platform-livedata/xwiki-platform-livedata-webjar/src/main/vue/src/components/LivedataDropdownMenu.vue

@@ -171,4 +171,16 @@ export default {
   text-align: center;
 }
 
+.livedata-dropdown-menu .dropdown-menu {
+  /* Dividers within the dropdown with an improved semantic representation */
+  li:has(> ul) + li:has(> ul) {
+    padding-top: calc(.5lh - 1px);
+    border-top: solid 1px var(--dropdown-divider-bg);
+  }
+
+  li:has(> ul):has(+ li > ul) {
+    margin-bottom: calc(.5lh - 1px);
+  }
+}
+
 </style>