enable shadows

packages/core/scss/bootstrap/_variables.scss

@@ -25,6 +25,13 @@ $warning-border-subtle:       mix(#fff, $warning, 70%) !default;
 $danger-border-subtle:        mix(#fff, $danger, 70%) !default;
 
 
+// Options
+//
+// Quickly modify global styling by enabling or disabling optional features.
+
+$enable-shadows: true;
+
+
 // Links
 //
 // Style anchor elements.