Merge pull request #14441 from Alhajras/issue/fix-the-tree-checkbox-c…

…ss-issue-and-make-it-clearer-when-it-is-disabled#14251

Fix the tree checkbox css issue and make it clearer when it is disabled

src/app/components/tree/tree.ts

@@ -103,7 +103,7 @@ import {
                             <ng-template *ngTemplateOutlet="tree.togglerIconTemplate; context: { $implicit: node.expanded }"></ng-template>
                         </span>
                     </button>
-                    <div class="p-checkbox p-component" [ngClass]="{ 'p-checkbox-disabled': node.selectable === false }" *ngIf="tree.selectionMode == 'checkbox'" aria-hidden="true">
+                    <div class="p-checkbox p-component" [ngClass]="{ 'p-checkbox-disabled p-disabled': node.selectable === false }" *ngIf="tree.selectionMode == 'checkbox'" aria-hidden="true">
                         <div class="p-checkbox-box" [ngClass]="{ 'p-highlight': isSelected(), 'p-indeterminate': node.partialSelected }" role="checkbox">
                             <ng-container *ngIf="!tree.checkboxIconTemplate">
                                 <CheckIcon *ngIf="!node.partialSelected && isSelected()" [styleClass]="'p-checkbox-icon'" />