Move blocks z-index up to match gui

Override the z-index for the blocks drag layer. At 1000, it will be over everything in the gui other than the navbar itself (monitors on the stage, tutorials, alerts, dropdown menus, etc.)

src/components/blocks/blocks.css

 @import "../../css/units.css";
 @import "../../css/colors.css";
+@import "../../css/z-index.css";
 
 .blocks {
     height: 100%;
@@ -80,6 +81,7 @@
         This does not prevent user interaction on the blocks themselves.
     */
     pointer-events: none;
+    z-index: $z-index-drag-layer; /* make blocks match gui drag layer */
 }
 
 /*

src/css/z-index.css

@@ -10,7 +10,6 @@ $z-index-stage-indicator: 45;
 $z-index-add-button: 46;
 $z-index-tooltip: 47; /* tooltips should go over add buttons if they overlap */
 $z-index-monitor: 48; /* monitors go over add buttons */
-/* Block drag z-index: 50; set in scratch-blocks */
 
 $z-index-card: 480;
 $z-index-alerts: 490;
@@ -19,6 +18,7 @@ $z-index-loader: 500;
 $z-index-modal: 510;
 
 $z-index-drag-layer: 1000;
+/* Block drag z-index: 1000; default 50 is overriden in blocks.css */
 $z-index-monitor-dragging: 1010;
 $z-index-dragging-sprite: 1020; /* so it is draggable into other panes */