Custom expression editor: make the I-beam cursor more subtle (#19294)

frontend/src/metabase/query_builder/components/expressions/expressions.css

@@ -11,3 +11,11 @@
 .ace-tm .ace_variable {
   color: var(--color-brand);
 }
+
+.ace_cursor {
+  border-left-width: 1px;
+}
+
+.ace_hidden-cursors .ace_cursor {
+  opacity: 0;
+}