Schema Diff Improvements:

1. Grid header should be center aligned vertically.
2. Increase the space between object counts.
3. The previous selected objects should not be re-selected on comparison.

web/pgadmin/tools/schema_diff/static/css/schema_diff.css

@@ -52,6 +52,7 @@
 
 .slick-header-column.ui-state-default {
     height: 32px !important;
+    line-height: 25px !important;
 }
 
 #schema-diff-grid .grid-header label {
@@ -187,3 +188,7 @@
   flex-wrap: wrap;
   max-width: 40% !important;
 }
+
+.slick-cell .ml-2 {
+  margin-left: 2rem !important;
+}