ENGCOM-4156: Rename LESS var names

Author: VladimirZaets

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/_panel.less

@@ -121,7 +121,7 @@
         user-select: none;
 
         .search-results-empty {
-            color: @color-darkie-gray;
+            color: @color-darker-gray;
             font-size: 12px;
             padding: 12px;
             text-align: center;
@@ -159,7 +159,7 @@
                 width: 100%;
             }
             a {
-                color: @color-darkie-gray;
+                color: @color-darker-gray;
                 display: inline-block;
                 font-size: 12px;
                 line-height: 16px;
@@ -192,7 +192,7 @@
             padding: 14px 10px;
 
             a {
-                color: @color-darkie-gray;
+                color: @color-darker-gray;
                 display: inline-block;
                 font-size: 12px;
                 line-height: 16px;