Merge pull request #18816 from overleaf/revert-18815-revert-18671-mj-left-modal

Revert "Revert "[web] Make left menu modal show below other modals""

GitOrigin-RevId: aaa51e251826c713ef0f46616ce8780d525d6430

services/web/frontend/stylesheets/app/editor/left-menu.less

@@ -191,11 +191,18 @@
   transition: opacity 0.5s;
 }
 
+// We want to be able to stack modals on top of the left-side menu. So we make
+// it a little lower than the normal modal backdrops. We don't want to go too
+// low, to avoid conflicting with dropdowns etc.
+@left-menu-z-index-backdrop: @zindex-modal-background - 5;
+@left-menu-z-index: @zindex-modal-background - 2;
+
 // Make the Bootstrap Modal behavior as a left sidebar
 #left-menu-modal {
   opacity: 1;
   overflow-y: hidden;
   padding-left: 0 !important; // bootstrap modal may randomly give padding-left when zooming in / out in chrome
+  z-index: @left-menu-z-index;
   .modal-dialog {
     height: 100%;
     margin: 0;
@@ -219,5 +226,6 @@
 // Don't disable backdrop that allows closing the Modal when clicking outside of it,
 // But match its background color with the original mask background color.
 .left-menu-modal-backdrop {
+  z-index: @left-menu-z-index-backdrop;
   background-color: transparent;
 }