move variable definition to pagetree file

packages/app/src/styles/_page-tree.scss

@@ -1,5 +1,8 @@
+$grw-sidebar-content-header-height: 58px;
+$grw-sidebar-content-footer-height: 50px;
+
 .grw-pagetree {
-  min-height: calc(100vh - ($grw-navbar-height + $grw-navbar-border-width + $grw-sidebar-content-header + $grw-sidebar-content-footer));
+  min-height: calc(100vh - ($grw-navbar-height + $grw-navbar-border-width + $grw-sidebar-content-header-height + $grw-sidebar-content-footer-height));
 
   .grw-pagetree-item {
     &:hover {

packages/app/src/styles/_variables.scss

@@ -25,8 +25,6 @@ $grw-navbar-bottom-height: 48px;
 $grw-editor-navbar-bottom-height: 48px;
 
 $grw-sidebar-nav-width: 64px; // !!DO NOT CHANGE!! 'margin-left' for '.css-teprsg' is hardcoded
-$grw-sidebar-content-header: 58px;
-$grw-sidebar-content-footer: 50px;
 
 $grw-logo-width: $grw-sidebar-nav-width;
 $grw-logomark-width: 36px;