diff --git a/DYImageView.m b/DYImageView.m
index 223dd80..5ccf7e5 100644
--- a/DYImageView.m
+++ b/DYImageView.m
@@ -54,8 +54,12 @@ - (float)zoomForFit {
 }
 
 - (void)drawRect:(NSRect)rect {
-	if (!image) return; //don't draw if nil
-	
+    // Always paint a black canvas first
+    [NSColor.blackColor set];
+    NSRectFill(self.bounds);
+
+    if (!image) return;
+
 	NSRect srcRect, destinationRect;
 	float zoom = zoomF;
 	NSRect boundsRect = [self convertRect:self.bounds toView:nil];
@@ -121,6 +125,7 @@ - (void)drawRect:(NSRect)rect {
 		destinationRect = [self convertRect:destinationRect fromView:nil];
 		[NSBezierPath fillRect:destinationRect];
 	}
+    destinationRect = NSIntegralRect(destinationRect);
 	NSGraphicsContext *cg = NSGraphicsContext.currentContext;
 	NSImageInterpolation oldInterp = cg.imageInterpolation;
 	cg.imageInterpolation = zoom >= 4 ? NSImageInterpolationNone : NSImageInterpolationHigh;
@@ -158,6 +163,10 @@ - (void)drawRect:(NSRect)rect {
 	}
 }
 
+- (BOOL)isOpaque {
+    return YES; // matches full-bounds black fill
+}
+
 - (void)animateGIF:(NSTimer *)t {
 	gifTimer = nil;
 	if (image != t.userInfo) return; // stop if image is changed
diff --git a/SlideshowWindow.m b/SlideshowWindow.m
index 62cd0e3..efc5533 100644
--- a/SlideshowWindow.m
+++ b/SlideshowWindow.m
@@ -21,6 +21,10 @@ static BOOL UsingMagicMouse(NSEvent *e) {
 
 @interface SlideshowWindow () <DYFileWatcherDelegate>
 @property (nonatomic, copy) NSComparator comparator;
+@property (nonatomic, strong) NSLayoutConstraint *imgL;
+@property (nonatomic, strong) NSLayoutConstraint *imgR;
+@property (nonatomic, strong) NSLayoutConstraint *imgT;
+@property (nonatomic, strong) NSLayoutConstraint *imgB;
 
 - (void)jump:(NSInteger)n;
 - (void)jumpTo:(NSUInteger)n;
@@ -95,21 +99,47 @@ - (instancetype)initWithContentRect:(NSRect)r styleMask:(NSWindowStyleMask)m bac
 		_upcomingQueue = [[NSOperationQueue alloc] init];
 		_fileWatcher = [[DYFileWatcher alloc] initWithDelegate:self];
 		
- 		self.backgroundColor = NSColor.blackColor;
-		self.opaque = NO;
+		self.backgroundColor = NSColor.blackColor;
+		self.opaque = YES;
 		_fullscreenMode = YES; // set this to prevent autosaving the frame from the nib
+		self.hasShadow = NO;
+		self.titlebarAppearsTransparent = YES;
+		self.titleVisibility = NSWindowTitleHidden;
 		self.collectionBehavior = NSWindowCollectionBehaviorParticipatesInCycle|NSWindowCollectionBehaviorFullScreenNone|NSWindowCollectionBehaviorMoveToActiveSpace;
 		// *** Unfortunately the menubar doesn't seem to show up on the second screen... Eventually we'll want to switch to use NSView's enterFullScreenMode:withOptions:
 		currentIndex = NSNotFound;
-   }
+	}
     return self;
 }
 
 - (void)awakeFromNib {
+	[super awakeFromNib];
+
 	imgView = [[DYImageView alloc] initWithFrame:NSZeroRect];
 	[self.contentView addSubview:imgView];
-	imgView.frame = self.contentView.frame;
-	imgView.autoresizingMask = NSViewWidthSizable | NSViewHeightSizable;
+
+	if (_fullscreenMode) {
+		// Fullscreen: constraint-driven
+		self.contentView.wantsLayer = YES;
+		self.contentView.layer.backgroundColor = NSColor.blackColor.CGColor;
+
+		imgView.translatesAutoresizingMaskIntoConstraints = NO;
+		NSLayoutGuide *clg = self.contentLayoutGuide;
+
+		self.imgL = [imgView.leadingAnchor constraintEqualToAnchor:clg.leadingAnchor];
+		self.imgR = [imgView.trailingAnchor constraintEqualToAnchor:clg.trailingAnchor];
+		self.imgT = [imgView.topAnchor constraintEqualToAnchor:clg.topAnchor];
+		self.imgB = [imgView.bottomAnchor constraintEqualToAnchor:clg.bottomAnchor];
+		[NSLayoutConstraint activateConstraints:@[self.imgL, self.imgR, self.imgT, self.imgB]];
+		// Notch avoidance (fullscreen) via constraints
+		[self applyNotchTopInsetForScreen:(self.visible ? self.screen : NSScreen.mainScreen)];
+	} else {
+		// Windowed: autoresizing-driven
+		self.contentView.wantsLayer = NO; // window background supplies black
+		imgView.translatesAutoresizingMaskIntoConstraints = YES;
+		imgView.autoresizingMask = NSViewWidthSizable | NSViewHeightSizable;
+		imgView.frame = self.contentView.bounds; // initial size only
+	}
 	
 	infoFld = [[NSTextField alloc] initWithFrame:NSMakeRect(0,0,360,20)];
 	[imgView addSubview:infoFld];
@@ -158,17 +188,94 @@ - (void)awakeFromNib {
 	}
 }
 
+/*
+ Developer note: Fullscreen vs windowed layout (macOS 26 grey-border fix)
+
+ - Fullscreen mode:
+   - Use Auto Layout constraints pinned to contentLayoutGuide on all edges.
+   - Make contentView layer-backed and paint black; window is opaque and shadowless.
+   - This avoids translucent composition that produced thin grey borders on macOS 26.
+   - Notch avoidance is applied via applyNotchTopInsetForScreen(screen), which offsets
+     the top constraint by safeAreaInsets.top when not ignored.
+
+ - Windowed mode:
+   - Disable constraints for imgView and rely on springs/struts (autoresizingMask).
+   - Keep contentView non-layer-backed; the window background provides black.
+   - Do not mix constraints and autoresizing; mixing caused subtle frame churn
+     and grey artifacts on macOS 26.
+
+ If you refactor this, keep the two systems mutually exclusive or move both modes
+ to constraints consistently. Always test fullscreen on notched displays to ensure
+ no grey edge reappears.
+*/
 - (void)setFullscreenMode:(BOOL)b {
-	_fullscreenMode = b;
-	if (b) {
-		self.styleMask = NSWindowStyleMaskBorderless;
-		self.collectionBehavior = NSWindowCollectionBehaviorParticipatesInCycle|NSWindowCollectionBehaviorFullScreenNone|NSWindowCollectionBehaviorMoveToActiveSpace;
-	} else {
-		self.styleMask = NSWindowStyleMaskTitled | NSWindowStyleMaskClosable | NSWindowStyleMaskResizable;
-		self.collectionBehavior = NSWindowCollectionBehaviorParticipatesInCycle|NSWindowCollectionBehaviorFullScreenNone|NSWindowCollectionBehaviorMoveToActiveSpace;
+    _fullscreenMode = b;
+
+    if (b) {
+        // Fullscreen window config
+        self.styleMask = NSWindowStyleMaskBorderless;
+        self.backgroundColor = NSColor.blackColor;   // solid canvas at the window level
+        self.opaque = YES;                           // avoid translucent composition
+        self.hasShadow = NO;
+        self.titlebarAppearsTransparent = YES;
+        self.titleVisibility = NSWindowTitleHidden;
+
+        // Layout system: constraints ON
+        self.contentView.wantsLayer = YES;
+        self.contentView.layer.backgroundColor = NSColor.blackColor.CGColor;
+
+        imgView.translatesAutoresizingMaskIntoConstraints = NO;
+        if (!self.imgL) {
+            NSLayoutGuide *clg = self.contentLayoutGuide;
+            self.imgL = [imgView.leadingAnchor constraintEqualToAnchor:clg.leadingAnchor];
+            self.imgR = [imgView.trailingAnchor constraintEqualToAnchor:clg.trailingAnchor];
+            self.imgT = [imgView.topAnchor constraintEqualToAnchor:clg.topAnchor];
+            self.imgB = [imgView.bottomAnchor constraintEqualToAnchor:clg.bottomAnchor];
+        }
+        [NSLayoutConstraint activateConstraints:@[self.imgL, self.imgR, self.imgT, self.imgB]];
+        // Notch avoidance (fullscreen) via constraints
+        [self applyNotchTopInsetForScreen:(self.visible ? self.screen : NSScreen.mainScreen)];
+        imgView.autoresizingMask = NSViewNotSizable;
+    } else {
+        // Windowed (titled) window config
+        self.styleMask = NSWindowStyleMaskTitled | NSWindowStyleMaskClosable | NSWindowStyleMaskResizable;
+        self.backgroundColor = NSColor.blackColor;   // black canvas from window
+        self.opaque = YES;                           // prevent Tahoe’s translucent treatment
+        self.hasShadow = YES;
+        self.titlebarAppearsTransparent = NO;
+        self.titleVisibility = NSWindowTitleVisible;
+
+        // Layout system: constraints OFF, autoresizing ON
+        if (self.imgL) {
+            [NSLayoutConstraint deactivateConstraints:@[self.imgL, self.imgR, self.imgT, self.imgB]];
+            self.imgL = self.imgR = self.imgT = self.imgB = nil;
+        }
+        self.contentView.wantsLayer = NO;
+        imgView.translatesAutoresizingMaskIntoConstraints = YES;
+        imgView.autoresizingMask = NSViewWidthSizable | NSViewHeightSizable;
+        imgView.frame = self.contentView.bounds; // reset initial size; autoresizing manages thereafter
+    }
+
+    self.collectionBehavior = NSWindowCollectionBehaviorParticipatesInCycle |
+                              NSWindowCollectionBehaviorFullScreenNone |
+                              NSWindowCollectionBehaviorMoveToActiveSpace;
+
+    [self.contentView layoutSubtreeIfNeeded]; // apply layout immediately
+    if (self.visible) [self configureScreen];
+}
+
+#pragma mark Notch avoidance
+// Centralized notch handling: offset top constraint by screen.safeAreaInsets.top when “pretendNotchIsntThere” is false.
+// This avoids placing content under the camera housing on notched displays in fullscreen.
+- (void)applyNotchTopInsetForScreen:(NSScreen *)screen {
+	if (!self.imgT) return;
+	CGFloat inset = 0.0;
+	if (@available(macOS 12.0, *)) {
+		if (![NSUserDefaults.standardUserDefaults boolForKey:@"pretendNotchIsntThere"]) {
+			inset = screen.safeAreaInsets.top;
+		}
 	}
-	if (self.visible)
-		[self configureScreen];
+	self.imgT.constant = inset;
 }
 
 - (void)setAutoRotate:(BOOL)b {
@@ -242,33 +349,29 @@ - (NSString *)currentShortFilename {
 	return s.length <= basePath.length ? s : [s substringFromIndex:basePath.length];
 }
 
-- (void)configureScreen // or rather, configure the window *for* the screen
-{
-	NSScreen *myScreen = self.visible ? self.screen : NSScreen.mainScreen;
-	NSRect screenRect = myScreen.frame;
-	if (_fullscreenMode) {
-		NSRect boundingRect = screenRect;
-		if (@available(macOS 12.0, *))
-			if (![NSUserDefaults.standardUserDefaults boolForKey:@"pretendNotchIsntThere"])
-				boundingRect.size.height -= myScreen.safeAreaInsets.top;
-		[self setFrame:screenRect display:NO];
-		boundingRect.origin = imgView.frame.origin;
-		imgView.frame = boundingRect;
-	} else {
-		NSString *v = [NSUserDefaults.standardUserDefaults objectForKey:@"DYSlideshowWindowFrame"];
-		NSRect r;
-		if (v) {
-			r = NSRectFromString(v);
-		} else {
-			// if no saved frame, put it in the top left of the screen
-			r = screenRect;
-			r.size.width = r.size.width/2;
-			r.size.height = r.size.height/2;
-			r.origin.y = screenRect.size.height;
-		}
-		[self setFrame:r display:NO];
-		imgView.frame = self.contentLayoutRect;
-	}
+- (void)configureScreen {
+    NSScreen *myScreen = self.visible ? self.screen : NSScreen.mainScreen;
+    NSRect screenRect = myScreen.frame;
+
+    if (_fullscreenMode) {
+        [self setFrame:screenRect display:NO];
+        // Notch avoidance (fullscreen) via constraints
+        [self applyNotchTopInsetForScreen:myScreen];
+        // Do NOT set imgView.frame here (constraints own it)
+    } else {
+        NSString *v = [NSUserDefaults.standardUserDefaults objectForKey:@"DYSlideshowWindowFrame"];
+        NSRect r;
+        if (v) {
+            r = NSRectFromString(v);
+        } else {
+            r = screenRect;
+            r.size.width  = r.size.width/2;
+            r.size.height = r.size.height/2;
+            r.origin.y    = screenRect.size.height;
+        }
+        [self setFrame:r display:NO];
+        // Do NOT set imgView.frame here; autoresizing owns it
+    }
 }
 
 - (void)configureBacking {