feat(ui_kit): use MultiColor in button style

packages/wyatt_ui_kit/lib/src/components/buttons/flat_button/flat_button.dart

@@ -40,20 +40,17 @@ class FlatButton extends FlatButtonComponent with $FlatButtonCWMixin {
 
   @override
   Widget build(BuildContext context) => Material(
+        color: const Color(0x00000000),
         child: Ink(
           decoration: BoxDecoration(
-            color: style?.backgroundColor ??
-                Theme.of(context).buttonTheme.colorScheme?.onPrimary,
-            gradient: LinearGradient(
-              colors: (style?.borderColors != null &&
-                      style!.borderColors!.length >= 2)
-                  ? style!.borderColors!
-                  : [
-                      // TODO(hpcl): change this
-                      Theme.of(context).cardColor,
-                      Theme.of(context).cardColor
-                    ],
-            ),
+            color: (style != null)
+                ? style!.backgroundColors?.color
+                : Theme.of(context).buttonTheme.colorScheme?.onPrimary,
+            gradient: (style?.backgroundColors?.isGradient ?? false)
+                ? LinearGradient(
+                    colors: style!.backgroundColors!.colors,
+                  )
+                : null,
             boxShadow: [
               if (style?.shadow != null) ...[style!.shadow!]
             ],

packages/wyatt_ui_kit/lib/src/components/buttons/outlined_button/outlined_button.dart

@@ -42,23 +42,20 @@ class OutlinedButton extends OutlinedButtonComponent
 
   @override
   Widget build(BuildContext context) => Material(
+        color: const Color(0x00000000),
         child: Ink(
           decoration: BoxDecoration(
-            color: style?.backgroundColor ??
-                Theme.of(context).buttonTheme.colorScheme?.onPrimary,
-            border: GradientBoxBorder(
-              gradient: LinearGradient(
-                colors: (style?.borderColors != null &&
-                        style!.borderColors!.length >= 2)
-                    ? style!.borderColors!
-                    : [
-                        // TODO(hpcl): change this
-                        Theme.of(context).cardColor,
-                        Theme.of(context).cardColor
-                      ],
-              ),
-              width: style?.stroke ?? 2,
-            ),
+            color: (style != null)
+                ? style!.backgroundColors?.color
+                : Theme.of(context).buttonTheme.colorScheme?.onPrimary,
+            border: (style?.borderColors?.isGradient ?? false)
+                ? GradientBoxBorder(
+                    gradient: LinearGradient(
+                      colors: style!.borderColors!.colors,
+                    ),
+                    width: style?.stroke ?? 2,
+                  )
+                : null,
             boxShadow: [
               if (style?.shadow != null) ...[style!.shadow!]
             ],