Adjust UI depth of query statistics

A z-index value of less than 1020 is needed because the time selection
dropdown shares the latter value via inheritance. Arbitrarily picked
1015 because it is a notch down.

Related: #14004

public/sass/pages/_explore.scss

@@ -165,7 +165,7 @@
   position: absolute;
   top: 0;
   right: 90px;
-  z-index: 1024;
+  z-index: 1015;
   display: flex;
   flex-direction: column;
   justify-content: center;