feat(card): use gray tokens

Author: thetaPC

core/src/components/card-subtitle/card-subtitle.ios.vars.scss

@@ -40,4 +40,4 @@ $card-ios-subtitle-margin-bottom: 4px;
 $card-ios-subtitle-margin-start: $card-ios-subtitle-margin-end;
 
 /// @prop - Color of the card subtitle
-$card-ios-subtitle-color: $text-color-step-400;
+$card-ios-subtitle-color: var(--ion-color-gray-600);

core/src/components/card-subtitle/card-subtitle.md.vars.scss

@@ -31,4 +31,4 @@ $card-md-subtitle-margin-bottom: 0;
 $card-md-subtitle-margin-start: $card-md-subtitle-margin-end;
 
 /// @prop - Color of the card subtitle
-$card-md-subtitle-color: $text-color-step-450;
+$card-md-subtitle-color: var(--ion-color-gray-550);

core/src/components/card-title/card-title.md.vars.scss

@@ -31,4 +31,4 @@ $card-md-title-margin-bottom: $card-md-title-margin-top;
 $card-md-title-margin-start: $card-md-title-margin-end;
 
 /// @prop - Color of the card title
-$card-md-title-text-color: $text-color-step-150;
+$card-md-title-text-color: var(--ion-color-gray-850);