feat(ios): add backgroundColor prop to top bar buttons

Add a new `backgroundColor` option to `OptionsTopBarButton` that sets a
solid color on the iOS 26 Liquid Glass circular platter behind React
component bar buttons.

All logic is guarded by @available(iOS 26.0, *) and a runtime check for
UIDesignRequiresCompatibility — when compatibility mode is enabled the
prop is ignored and the button renders as before.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: IsaacIsrael

ios/RNNButtonOptions.h

@@ -24,6 +24,7 @@
 @property(nonatomic, strong) RNNIconBackgroundOptions *iconBackground;
 @property(nonatomic, strong) Bool *disableIconTint;
 @property(nonatomic, strong) Bool *hideSharedBackground;
+@property(nonatomic, strong) Color *backgroundColor;
 
 - (RNNButtonOptions *)withDefault:(RNNButtonOptions *)defaultOptions;
 

ios/RNNReactButtonView.mm

@@ -63,6 +63,15 @@ - (void)updateConstraintsToFitSize {
     }
 }
 
+- (void)didMoveToWindow {
+    [super didMoveToWindow];
+    if (@available(iOS 26.0, *)) {
+        if (![self designRequiresCompatibility] && self.window) {
+            [self syncButtonBackground];
+        }
+    }
+}
+
 - (void)layoutSubviews {
     [super layoutSubviews];
     if (@available(iOS 26.0, *)) {
@@ -76,9 +85,21 @@ - (void)layoutSubviews {
                 self.layer.affineTransform = CGAffineTransformMakeTranslation(tx, 0);
             }
         }
+        [self syncButtonBackground];
     }
 }
 
+- (void)syncButtonBackground {
+    if (!_buttonBackgroundColor) return;
+
+    UIView *target = self.superview.superview.superview;
+    if (!target || target.bounds.size.height <= 0) return;
+
+    target.backgroundColor = _buttonBackgroundColor;
+    target.layer.cornerRadius = target.bounds.size.height / 2.0;
+    target.clipsToBounds = YES;
+}
+
 - (NSString *)componentType {
 	return ComponentTypeButton;
 }

src/interfaces/Options.ts

@@ -658,6 +658,13 @@ export interface OptionsTopBarButton {
    * @see {@link https://developer.android.com/guide/topics/resources/menu-resource|Android developer guide: Menu resource}
    */
   showAsAction?: 'ifRoom' | 'withText' | 'always' | 'never';
+  /**
+   * (iOS 26+ only) Set a solid background color on the circular Liquid Glass
+   * platter behind the button. Ignored when UIDesignRequiresCompatibility is
+   * enabled or on iOS < 26.
+   * #### (iOS specific)
+   */
+  backgroundColor?: Color;
 }
 
 export interface OptionsSearchBar {