fix(card): update background to use the same as item (#19602)

uses item background but falls back to the background of the content

Author: brandyscarney

core/src/components/card/card.ios.scss

@@ -5,7 +5,7 @@
 // --------------------------------------------------
 
 :host {
-  --background: var(--ion-item-background, transparent);
+  --background: #{$item-ios-background};
   --color: #{$card-ios-text-color};
 
   @include margin($card-ios-margin-top, $card-ios-margin-end, $card-ios-margin-bottom, $card-ios-margin-start);

core/src/components/card/card.md.scss

@@ -5,7 +5,7 @@
 // --------------------------------------------------
 
 :host {
-  --background: var(--ion-item-background, transparent);
+  --background: #{$item-md-background};
   --color: #{$card-md-text-color};
 
   @include margin($card-md-margin-top, $card-md-margin-end, $card-md-margin-bottom, $card-md-margin-start);