fix: add card shadow to onboarding widget (#21031) (#21032)

Contrast between bg and widget was very low added shadow so it's
slightly more noticable.

[skip ci]

(cherry picked from commit badcd7a)

Co-authored-by: Ankush Menat <ankush@frappe.io>

frappe/public/scss/desk/desktop.scss

@@ -342,6 +342,7 @@ body {
 		margin-bottom: var(--margin-2xl);
 		padding: var(--padding-lg) !important;
 		background-color: var(--bg-color);
+		box-shadow: var(--card-shadow) ;
 
 		&.edit-mode:hover {
 			background-color: var(--fg-color);