fix: add legacy glass fallback surfaces

Provide a shared pre-iOS 26/macOS 26/tvOS 26 fallback for glass-style buttons and glassEffect surfaces so overlay controls remain readable on older systems.

Also update the UIKit end-page close button path to use a matching background treatment, including reduce-transparency fallbacks.

Author: everpcpc

KMReader/Features/Reader/Views/EndPageCloseButtonStyle.swift

@@ -20,7 +20,27 @@
           return .glass()
         }
       #endif
-      return .bordered()
+      var configuration = UIButton.Configuration.bordered()
+      var background = UIBackgroundConfiguration.clear()
+      #if os(iOS)
+        if UIAccessibility.isReduceTransparencyEnabled {
+          background.backgroundColor = .systemBackground.withAlphaComponent(0.96)
+          background.strokeColor = UIColor.label.withAlphaComponent(0.12)
+        } else {
+          background.visualEffect = UIBlurEffect(style: .systemMaterial)
+          background.strokeColor = UIColor.white.withAlphaComponent(0.24)
+        }
+      #elseif os(tvOS)
+        background.backgroundColor = UIColor.black.withAlphaComponent(
+          UIAccessibility.isReduceTransparencyEnabled ? 0.92 : 0.76
+        )
+        background.strokeColor = UIColor.white.withAlphaComponent(
+          UIAccessibility.isReduceTransparencyEnabled ? 0.18 : 0.24
+        )
+      #endif
+      background.strokeWidth = 1
+      configuration.background = background
+      return configuration
     }
 
     private static var buttonSymbolConfiguration: UIImage.SymbolConfiguration {

KMReader/Shared/Extensions/View+ButtonStyle.swift

@@ -17,6 +17,66 @@ enum GlassEffectType {
   case regular
 }
 
+private struct LegacyGlassSurfaceModifier<SurfaceShape: Shape>: ViewModifier {
+  @Environment(\.accessibilityReduceTransparency) private var reduceTransparency
+
+  let type: GlassEffectType
+  let shape: SurfaceShape
+
+  func body(content: Content) -> some View {
+    content
+      .background(backgroundStyle, in: shape)
+      .overlay {
+        shape
+          .stroke(borderColor, lineWidth: reduceTransparency ? 1 : 0.8)
+      }
+      .shadow(
+        color: reduceTransparency ? .clear : .black.opacity(type == .clear ? 0.08 : 0.14),
+        radius: type == .clear ? 4 : 8,
+        x: 0,
+        y: 2
+      )
+  }
+
+  private var backgroundStyle: AnyShapeStyle {
+    if reduceTransparency {
+      return AnyShapeStyle(reducedTransparencyColor)
+    }
+
+    switch type {
+    case .clear:
+      return AnyShapeStyle(.ultraThinMaterial)
+    case .regular:
+      return AnyShapeStyle(.regularMaterial)
+    }
+  }
+
+  private var borderColor: Color {
+    if reduceTransparency {
+      return .primary.opacity(0.12)
+    }
+
+    switch type {
+    case .clear:
+      return .white.opacity(0.18)
+    case .regular:
+      return .white.opacity(0.24)
+    }
+  }
+
+  private var reducedTransparencyColor: Color {
+    #if os(iOS)
+      return type == .clear ? Color(.secondarySystemBackground) : Color(.systemBackground)
+    #elseif os(tvOS)
+      return type == .clear ? Color.black.opacity(0.84) : Color.black.opacity(0.92)
+    #elseif os(macOS)
+      return type == .clear ? Color(NSColor.windowBackgroundColor) : Color(NSColor.controlBackgroundColor)
+    #else
+      return .gray
+    #endif
+  }
+}
+
 extension View {
   @ViewBuilder
   func adaptiveButtonStyle(_ style: AdaptiveButtonStyleType) -> some View {
@@ -48,9 +108,13 @@ extension View {
       case .borderedProminent:
         self.buttonStyle(.borderedProminent)
       case .bordered:
-        self.buttonStyle(.bordered)
+        self
+          .buttonStyle(.bordered)
+          .legacyGlassSurface(.regular, in: ButtonBorderShape.buttonBorder)
       case .borderless:
-        self.buttonStyle(.borderless)
+        self
+          .buttonStyle(.borderless)
+          .legacyGlassSurface(.regular, in: ButtonBorderShape.buttonBorder)
       case .plain:
         #if os(tvOS)
           self.buttonStyle(.card)
@@ -74,7 +138,7 @@ extension View {
         case .regular: self.glassEffect(.regular)
         }
       } else {
-        self
+        self.legacyGlassSurface(type, in: RoundedRectangle(cornerRadius: 16, style: .continuous))
       }
     } else {
       self
@@ -92,10 +156,14 @@ extension View {
         case .regular: self.glassEffect(.regular, in: shape)
         }
       } else {
-        self
+        self.legacyGlassSurface(type, in: shape)
       }
     } else {
       self
     }
   }
+
+  private func legacyGlassSurface<S: Shape>(_ type: GlassEffectType, in shape: S) -> some View {
+    modifier(LegacyGlassSurfaceModifier(type: type, shape: shape))
+  }
 }