diff --git a/web/src/components/MotionPhotoPreview.tsx b/web/src/components/MotionPhotoPreview.tsx
index f3627b8ca..69b9510f9 100644
--- a/web/src/components/MotionPhotoPreview.tsx
+++ b/web/src/components/MotionPhotoPreview.tsx
@@ -41,10 +41,11 @@ const MotionPhotoPreview = ({
         containerClassName={cn("max-w-full max-h-full", containerClassName)}
         mediaClassName={mediaClassName}
       />
-      <button
-        type="button"
+      <div
+        role="button"
+        tabIndex={0}
         className={cn(
-          "absolute rounded-full border border-border/45 bg-background/65 px-2.5 py-1 text-xs font-semibold tracking-wide text-foreground backdrop-blur-sm transition-colors hover:bg-background/80 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring/50",
+          "absolute select-none rounded-full border border-border/45 bg-background/65 px-2.5 py-1 text-xs font-semibold tracking-wide text-foreground backdrop-blur-sm transition-colors hover:bg-background/80 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring/50",
           badgeClassName,
         )}
         onMouseEnter={() => setMotionActive(true)}
@@ -64,10 +65,16 @@ const MotionPhotoPreview = ({
           }
         }}
         onPointerCancel={() => setMotionActive(false)}
+        onKeyDown={(event) => {
+          if (event.key === "Enter" || event.key === " ") {
+            event.preventDefault();
+            setMotionActive((prev) => !prev);
+          }
+        }}
         aria-label="Hover or press to play live photo"
       >
         LIVE
-      </button>
+      </div>
     </div>
   );
 };
diff --git a/web/src/components/PreviewImageDialog.tsx b/web/src/components/PreviewImageDialog.tsx
index 3e6c8b459..303eb4c0d 100644
--- a/web/src/components/PreviewImageDialog.tsx
+++ b/web/src/components/PreviewImageDialog.tsx
@@ -1,8 +1,11 @@
-import { X } from "lucide-react";
-import React, { useEffect, useState } from "react";
+import { ChevronLeft, ChevronRight, X } from "lucide-react";
+import React, { useEffect, useMemo, useState } from "react";
 import MotionPhotoPreview from "@/components/MotionPhotoPreview";
 import { Button } from "@/components/ui/button";
-import { Dialog, DialogContent } from "@/components/ui/dialog";
+import { Dialog, DialogContent, DialogTitle } from "@/components/ui/dialog";
+import { VisuallyHidden } from "@/components/ui/visually-hidden";
+import useMediaQuery from "@/hooks/useMediaQuery";
+import { cn } from "@/lib/utils";
 import type { PreviewMediaItem } from "@/utils/media-item";
 
 interface Props {
@@ -14,115 +17,216 @@ interface Props {
 }
 
 function PreviewImageDialog({ open, onOpenChange, imgUrls = [], items, initialIndex = 0 }: Props) {
+  const sm = useMediaQuery("sm");
   const [currentIndex, setCurrentIndex] = useState(initialIndex);
-  const previewItems =
-    items ?? imgUrls.map((url) => ({ id: url, kind: "image" as const, sourceUrl: url, posterUrl: url, filename: "Image" }));
+  const previewItems = useMemo(
+    () => items ?? imgUrls.map((url) => ({ id: url, kind: "image" as const, sourceUrl: url, posterUrl: url, filename: "Image" })),
+    [imgUrls, items],
+  );
 
-  // Update current index when initialIndex prop changes
   useEffect(() => {
-    setCurrentIndex(initialIndex);
-  }, [initialIndex]);
+    if (open) {
+      setCurrentIndex(initialIndex);
+    }
+  }, [initialIndex, open]);
+
+  const itemCount = previewItems.length;
+  const safeIndex = Math.max(0, Math.min(currentIndex, itemCount - 1));
+  const currentItem = previewItems[safeIndex];
+  const hasMultiple = itemCount > 1;
+  const canGoPrevious = safeIndex > 0;
+  const canGoNext = safeIndex < itemCount - 1;
 
-  // Handle keyboard navigation
   useEffect(() => {
     const handleKeyDown = (event: KeyboardEvent) => {
-      if (!open) return;
+      if (!open) {
+        return;
+      }
 
-      switch (event.key) {
-        case "Escape":
-          onOpenChange(false);
-          break;
-        case "ArrowRight":
-          setCurrentIndex((prev) => Math.min(prev + 1, previewItems.length - 1));
-          break;
-        case "ArrowLeft":
-          setCurrentIndex((prev) => Math.max(prev - 1, 0));
-          break;
-        default:
-          break;
+      if (event.key === "Escape") {
+        onOpenChange(false);
+        return;
+      }
+
+      if (event.key === "ArrowLeft") {
+        setCurrentIndex((prev) => Math.max(prev - 1, 0));
+        return;
+      }
+
+      if (event.key === "ArrowRight") {
+        setCurrentIndex((prev) => Math.min(prev + 1, itemCount - 1));
       }
     };
 
     document.addEventListener("keydown", handleKeyDown);
     return () => document.removeEventListener("keydown", handleKeyDown);
-  }, [open, onOpenChange]);
+  }, [itemCount, onOpenChange, open]);
 
-  const handleClose = () => {
-    onOpenChange(false);
-  };
+  if (!itemCount || !currentItem) {
+    return null;
+  }
 
-  const handleBackdropClick = (event: React.MouseEvent<HTMLDivElement>) => {
-    if (event.target === event.currentTarget) {
-      handleClose();
-    }
-  };
-
-  // Return early if no images provided
-  if (!previewItems.length) return null;
-
-  // Ensure currentIndex is within bounds
-  const safeIndex = Math.max(0, Math.min(currentIndex, previewItems.length - 1));
-  const currentItem = previewItems[safeIndex];
+  const handleClose = () => onOpenChange(false);
+  const handlePrevious = () => setCurrentIndex((prev) => Math.max(prev - 1, 0));
+  const handleNext = () => setCurrentIndex((prev) => Math.min(prev + 1, itemCount - 1));
 
   return (
     <Dialog open={open} onOpenChange={onOpenChange}>
       <DialogContent
-        className="!w-[100vw] !h-[100vh] !max-w-[100vw] !max-h-[100vw] p-0 border-0 shadow-none bg-transparent [&>button]:hidden"
+        showCloseButton={false}
+        className="!h-[100vh] !w-[100vw] !max-h-[100vh] !max-w-[100vw] overflow-hidden border-0 bg-black/92 p-0 shadow-none"
         aria-describedby="image-preview-description"
       >
-        {/* Close button */}
-        <div className="fixed top-4 right-4 z-50">
-          <Button
-            onClick={handleClose}
-            variant="secondary"
-            size="icon"
-            className="rounded-full bg-popover/20 hover:bg-popover/30 border-border/20 backdrop-blur-sm"
-            aria-label="Close image preview"
-          >
-            <X className="h-4 w-4 text-popover-foreground" />
-          </Button>
+        <VisuallyHidden>
+          <DialogTitle>{currentItem.filename || "Attachment preview"}</DialogTitle>
+        </VisuallyHidden>
+
+        <div className="absolute inset-x-0 top-0 z-20 bg-linear-to-b from-black/70 via-black/35 to-transparent px-3 pb-6 pt-3 sm:px-5 sm:pt-4">
+          <div className="flex items-start justify-between gap-3">
+            <div className="min-w-0 text-white">
+              <div className="truncate text-sm font-medium">{currentItem.filename || "Attachment"}</div>
+              {hasMultiple && (
+                <div className="mt-1 text-xs text-white/70">
+                  {safeIndex + 1} / {itemCount}
+                </div>
+              )}
+            </div>
+
+            <Button
+              type="button"
+              onClick={handleClose}
+              variant="ghost"
+              size="icon"
+              className="shrink-0 rounded-full bg-white/10 text-white hover:bg-white/16 hover:text-white"
+              aria-label="Close preview"
+            >
+              <X className="h-4 w-4" />
+            </Button>
+          </div>
         </div>
 
-        {/* Image container */}
-        <div className="w-full h-full flex items-center justify-center p-4 sm:p-8 overflow-auto" onClick={handleBackdropClick}>
-          {currentItem.kind === "video" ? (
-            <video
-              key={currentItem.id}
-              src={currentItem.sourceUrl}
-              poster={currentItem.posterUrl}
-              className="max-w-full max-h-full object-contain"
-              controls
-              autoPlay
-            />
-          ) : currentItem.kind === "motion" ? (
-            <MotionPhotoPreview
-              key={currentItem.id}
-              posterUrl={currentItem.posterUrl}
-              motionUrl={currentItem.motionUrl}
-              alt={`Preview live photo ${safeIndex + 1} of ${previewItems.length}`}
-              presentationTimestampUs={currentItem.presentationTimestampUs}
-              badgeClassName="left-4 top-4"
-              mediaClassName="max-h-[calc(100vh-2rem)] max-w-[calc(100vw-2rem)] object-contain sm:max-h-[calc(100vh-4rem)] sm:max-w-[calc(100vw-4rem)]"
-            />
-          ) : (
-            <img
-              src={currentItem.sourceUrl}
-              alt={`Preview image ${safeIndex + 1} of ${previewItems.length}`}
-              className="max-w-full max-h-full object-contain select-none"
-              draggable={false}
-              loading="eager"
-              decoding="async"
-            />
-          )}
+        <div
+          className="flex h-full w-full items-center justify-center px-3 pb-20 pt-16 sm:px-16 sm:pb-8 sm:pt-20"
+          onClick={(event) => {
+            if (event.target === event.currentTarget) {
+              handleClose();
+            }
+          }}
+        >
+          <div className="flex max-h-full max-w-full items-center justify-center" onClick={(event) => event.stopPropagation()}>
+            {currentItem.kind === "video" ? (
+              <video
+                key={currentItem.id}
+                src={currentItem.sourceUrl}
+                poster={currentItem.posterUrl}
+                className="max-h-[calc(100vh-8rem)] max-w-[calc(100vw-1.5rem)] rounded-md object-contain sm:max-h-[calc(100vh-7rem)] sm:max-w-[calc(100vw-8rem)]"
+                controls
+                autoPlay
+                playsInline
+              />
+            ) : currentItem.kind === "motion" ? (
+              <MotionPhotoPreview
+                key={currentItem.id}
+                posterUrl={currentItem.posterUrl}
+                motionUrl={currentItem.motionUrl}
+                alt={`Preview live photo ${safeIndex + 1} of ${itemCount}`}
+                presentationTimestampUs={currentItem.presentationTimestampUs}
+                badgeClassName="left-3 top-3 sm:left-4 sm:top-4"
+                mediaClassName="max-h-[calc(100vh-8rem)] max-w-[calc(100vw-1.5rem)] rounded-md object-contain sm:max-h-[calc(100vh-7rem)] sm:max-w-[calc(100vw-8rem)]"
+              />
+            ) : (
+              <img
+                src={currentItem.sourceUrl}
+                alt={`Preview image ${safeIndex + 1} of ${itemCount}`}
+                className="max-h-[calc(100vh-8rem)] max-w-[calc(100vw-1.5rem)] rounded-md object-contain select-none sm:max-h-[calc(100vh-7rem)] sm:max-w-[calc(100vw-8rem)]"
+                draggable={false}
+                loading="eager"
+                decoding="async"
+              />
+            )}
+          </div>
         </div>
 
-        {/* Screen reader description */}
+        {hasMultiple && sm && (
+          <>
+            <NavButton
+              side="left"
+              disabled={!canGoPrevious}
+              label="Previous item"
+              onClick={handlePrevious}
+              icon={<ChevronLeft className="h-5 w-5" />}
+            />
+            <NavButton
+              side="right"
+              disabled={!canGoNext}
+              label="Next item"
+              onClick={handleNext}
+              icon={<ChevronRight className="h-5 w-5" />}
+            />
+          </>
+        )}
+
+        {hasMultiple && !sm && (
+          <div className="absolute inset-x-0 bottom-0 z-20 px-3 pb-3 pt-6">
+            <div className="mx-auto flex max-w-xs items-center justify-between rounded-full bg-black/55 px-2 py-2 backdrop-blur-sm">
+              <Button
+                type="button"
+                variant="ghost"
+                size="sm"
+                onClick={handlePrevious}
+                disabled={!canGoPrevious}
+                className="rounded-full px-3 text-white hover:bg-white/10 hover:text-white disabled:text-white/35"
+              >
+                Prev
+              </Button>
+              <div className="px-3 text-xs text-white/75">
+                {safeIndex + 1} / {itemCount}
+              </div>
+              <Button
+                type="button"
+                variant="ghost"
+                size="sm"
+                onClick={handleNext}
+                disabled={!canGoNext}
+                className="rounded-full px-3 text-white hover:bg-white/10 hover:text-white disabled:text-white/35"
+              >
+                Next
+              </Button>
+            </div>
+          </div>
+        )}
+
         <div id="image-preview-description" className="sr-only">
-          Attachment preview dialog. Press Escape to close or click outside the media.
+          Attachment preview dialog. Press Escape to close and use left or right arrow keys to switch items.
         </div>
       </DialogContent>
     </Dialog>
   );
 }
 
+interface NavButtonProps {
+  side: "left" | "right";
+  disabled: boolean;
+  label: string;
+  onClick: () => void;
+  icon: React.ReactNode;
+}
+
+const NavButton = ({ side, disabled, label, onClick, icon }: NavButtonProps) => (
+  <Button
+    type="button"
+    variant="ghost"
+    size="icon"
+    disabled={disabled}
+    onClick={onClick}
+    aria-label={label}
+    className={cn(
+      "absolute top-1/2 z-20 hidden h-11 w-11 -translate-y-1/2 rounded-full bg-white/10 text-white backdrop-blur-sm hover:bg-white/16 hover:text-white disabled:opacity-25 sm:flex",
+      side === "left" ? "left-4" : "right-4",
+    )}
+  >
+    {icon}
+  </Button>
+);
+
 export default PreviewImageDialog;