fix: plain style background to use color clear

Author: danielnordh

Sources/BitcoinUI/ButtonStyles.swift

@@ -199,14 +199,11 @@ public struct BitcoinPlain: ButtonStyle {
             .font(Font.body.bold())
             .padding()
             .frame(width: width, height: height)
-            .background(stateBackgroundColor())
+            .background(Color.clear)
             .foregroundColor(stateTextColor())
             .scaleEffect(configuration.isPressed ? 0.95 : 1)
             .animation(.easeOut(duration: 0.1), value: configuration.isPressed)
     }
-    private func stateBackgroundColor() -> Color {
-        return colorScheme == .dark ? .bitcoinBlack : .bitcoinWhite
-    }
     private func stateBorderColor(configuration: Configuration) -> Color {
         return isEnabled
             ? configuration.isPressed ? tintColor.opacity(0.8) : tintColor : disabledColor