[DDW-1011] level loading backdrop with table header

Author: shawnbusuttil

source/renderer/app/components/staking/stake-pools/StakePoolsRankingLoader.scss

@@ -1,3 +1,5 @@
+@import '../../../themes/mixins/layers.scss';
+
 .component {
   align-items: center;
   background-color: var(--rp-modal-overlay-bg-color);
@@ -8,4 +10,5 @@
   position: fixed;
   right: 0;
   top: 134px;
+  z-index: $loader-backdrop-z-index;
 }

source/renderer/app/components/staking/stake-pools/StakePoolsTable.scss

@@ -1,5 +1,6 @@
 @import '../../../themes/mixins/link';
 @import '../../../themes/mixins/loading-spinner';
+@import '../../../themes/mixins/layers';
 
 .component {
   .headerWrapper {
@@ -105,7 +106,7 @@
       padding: 0 20px;
       position: sticky;
       top: 0;
-      z-index: 1;
+      z-index: $sticky-header-z-index;
 
       tr {
         border: 0;

source/renderer/app/themes/mixins/layers.scss

@@ -1 +1,3 @@
 $dialog-z-index: 200;
+$loader-backdrop-z-index: 5;
+$sticky-header-z-index: 1;