Refactor Material UI's box-shadow style to match our scss linter

src/styles/index.scss

@@ -115,10 +115,14 @@
 // override react-mosaic styles to mimic MUI's elevation
 .mosaic {
   &-tile {
-    box-shadow: 0px 1px 3px 0px rgba(0,0,0,0.2),0px 1px 1px 0px rgba(0,0,0,0.14),0px 2px 1px -1px rgba(0,0,0,0.12);
+    $start: rgba(0, 0, 0, .2);
+    $middle: rgba(0, 0, 0, .2);
+    $end: rgba(0, 0, 0, .2);
+    box-shadow: 0 1px 3px 0 $start, 0 1px 1px 0 $middle, 0 2px 1px -1px $end;
   }
 
-  &-window, &-preview {
+  &-window,
+  &-preview {
     box-shadow: none;
   }
 }