diff --git a/extensions/diffs/src/render.ts b/extensions/diffs/src/render.ts
index 5360b2f46c7..fb3d089c90a 100644
--- a/extensions/diffs/src/render.ts
+++ b/extensions/diffs/src/render.ts
@@ -150,6 +150,16 @@ function buildImageRenderOptions(options: DiffRenderOptions): DiffRenderOptions
   };
 }
 
+function buildRenderVariants(options: DiffRenderOptions): {
+  viewerOptions: DiffViewerOptions;
+  imageOptions: DiffViewerOptions;
+} {
+  return {
+    viewerOptions: buildDiffOptions(options),
+    imageOptions: buildDiffOptions(buildImageRenderOptions(options)),
+  };
+}
+
 function normalizeSupportedLanguage(value?: string): SupportedLanguages | undefined {
   const normalized = value?.trim();
   return normalized ? (normalized as SupportedLanguages) : undefined;
@@ -298,6 +308,35 @@ function buildHtmlDocument(params: {
 </html>`;
 }
 
+type RenderedSection = {
+  viewer: string;
+  image: string;
+};
+
+function buildRenderedSection(params: {
+  viewerPrerenderedHtml: string;
+  imagePrerenderedHtml: string;
+  payload: Omit<DiffViewerPayload, "prerenderedHTML">;
+}): RenderedSection {
+  return {
+    viewer: renderDiffCard({
+      prerenderedHTML: params.viewerPrerenderedHtml,
+      ...params.payload,
+    }),
+    image: renderStaticDiffCard(params.imagePrerenderedHtml),
+  };
+}
+
+function buildRenderedBodies(sections: ReadonlyArray<RenderedSection>): {
+  viewerBodyHtml: string;
+  imageBodyHtml: string;
+} {
+  return {
+    viewerBodyHtml: sections.map((section) => section.viewer).join("\n"),
+    imageBodyHtml: sections.map((section) => section.image).join("\n"),
+  };
+}
+
 async function renderBeforeAfterDiff(
   input: Extract<DiffInput, { kind: "before_after" }>,
   options: DiffRenderOptions,
@@ -314,33 +353,35 @@ async function renderBeforeAfterDiff(
     contents: input.after,
     ...(lang ? { lang } : {}),
   };
-  const viewerPayloadOptions = buildDiffOptions(options);
-  const imagePayloadOptions = buildDiffOptions(buildImageRenderOptions(options));
+  const { viewerOptions, imageOptions } = buildRenderVariants(options);
   const [viewerResult, imageResult] = await Promise.all([
     preloadMultiFileDiff({
       oldFile,
       newFile,
-      options: viewerPayloadOptions,
+      options: viewerOptions,
     }),
     preloadMultiFileDiff({
       oldFile,
       newFile,
-      options: imagePayloadOptions,
+      options: imageOptions,
     }),
   ]);
-
-  return {
-    viewerBodyHtml: renderDiffCard({
-      prerenderedHTML: viewerResult.prerenderedHTML,
+  const section = buildRenderedSection({
+    viewerPrerenderedHtml: viewerResult.prerenderedHTML,
+    imagePrerenderedHtml: imageResult.prerenderedHTML,
+    payload: {
       oldFile: viewerResult.oldFile,
       newFile: viewerResult.newFile,
-      options: viewerPayloadOptions,
+      options: viewerOptions,
       langs: buildPayloadLanguages({
         oldFile: viewerResult.oldFile,
         newFile: viewerResult.newFile,
       }),
-    }),
-    imageBodyHtml: renderStaticDiffCard(imageResult.prerenderedHTML),
+    },
+  });
+
+  return {
+    ...buildRenderedBodies([section]),
     fileCount: 1,
   };
 }
@@ -365,36 +406,34 @@ async function renderPatchDiff(
     throw new Error(`Patch input is too large to render (max ${MAX_PATCH_TOTAL_LINES} lines).`);
   }
 
-  const viewerPayloadOptions = buildDiffOptions(options);
-  const imagePayloadOptions = buildDiffOptions(buildImageRenderOptions(options));
+  const { viewerOptions, imageOptions } = buildRenderVariants(options);
   const sections = await Promise.all(
     files.map(async (fileDiff) => {
       const [viewerResult, imageResult] = await Promise.all([
         preloadFileDiff({
           fileDiff,
-          options: viewerPayloadOptions,
+          options: viewerOptions,
         }),
         preloadFileDiff({
           fileDiff,
-          options: imagePayloadOptions,
+          options: imageOptions,
         }),
       ]);
 
-      return {
-        viewer: renderDiffCard({
-          prerenderedHTML: viewerResult.prerenderedHTML,
+      return buildRenderedSection({
+        viewerPrerenderedHtml: viewerResult.prerenderedHTML,
+        imagePrerenderedHtml: imageResult.prerenderedHTML,
+        payload: {
           fileDiff: viewerResult.fileDiff,
-          options: viewerPayloadOptions,
+          options: viewerOptions,
           langs: buildPayloadLanguages({ fileDiff: viewerResult.fileDiff }),
-        }),
-        image: renderStaticDiffCard(imageResult.prerenderedHTML),
-      };
+        },
+      });
     }),
   );
 
   return {
-    viewerBodyHtml: sections.map((section) => section.viewer).join("\n"),
-    imageBodyHtml: sections.map((section) => section.image).join("\n"),
+    ...buildRenderedBodies(sections),
     fileCount: files.length,
   };
 }
diff --git a/extensions/diffs/src/tool.ts b/extensions/diffs/src/tool.ts
index 862fd2b0d56..1578c6e1e36 100644
--- a/extensions/diffs/src/tool.ts
+++ b/extensions/diffs/src/tool.ts
@@ -187,9 +187,10 @@ export function createDiffsTool(params: {
           content: [
             {
               type: "text",
-              text:
-                `Diff ${image.format.toUpperCase()} generated at: ${artifactFile.path}\n` +
-                "Use the `message` tool with `path` or `filePath` to send this file.",
+              text: buildFileArtifactMessage({
+                format: image.format,
+                filePath: artifactFile.path,
+              }),
             },
           ],
           details: buildArtifactDetails({
@@ -257,10 +258,11 @@ export function createDiffsTool(params: {
           content: [
             {
               type: "text",
-              text:
-                `Diff viewer: ${viewerUrl}\n` +
-                `Diff ${image.format.toUpperCase()} generated at: ${artifactFile.path}\n` +
-                "Use the `message` tool with `path` or `filePath` to send this file.",
+              text: buildFileArtifactMessage({
+                format: image.format,
+                filePath: artifactFile.path,
+                viewerUrl,
+              }),
             },
           ],
           details: buildArtifactDetails({
@@ -330,6 +332,17 @@ function buildArtifactDetails(params: {
   };
 }
 
+function buildFileArtifactMessage(params: {
+  format: DiffOutputFormat;
+  filePath: string;
+  viewerUrl?: string;
+}): string {
+  const lines = params.viewerUrl ? [`Diff viewer: ${params.viewerUrl}`] : [];
+  lines.push(`Diff ${params.format.toUpperCase()} generated at: ${params.filePath}`);
+  lines.push("Use the `message` tool with `path` or `filePath` to send this file.");
+  return lines.join("\n");
+}
+
 async function renderDiffArtifactFile(params: {
   screenshotter: DiffScreenshotter;
   store: DiffArtifactStore;
diff --git a/extensions/diffs/src/viewer-client.ts b/extensions/diffs/src/viewer-client.ts
index 8e54c298bc7..14ffaed7cbd 100644
--- a/extensions/diffs/src/viewer-client.ts
+++ b/extensions/diffs/src/viewer-client.ts
@@ -106,39 +106,9 @@ function createToolbarButton(params: {
 }
 
 function applyToolbarButtonStyles(button: HTMLButtonElement, active: boolean): void {
-  button.style.display = "inline-flex";
-  button.style.alignItems = "center";
-  button.style.justifyContent = "center";
-  button.style.width = "24px";
-  button.style.height = "24px";
-  button.style.padding = "0";
-  button.style.margin = "0";
-  button.style.border = "0";
-  button.style.borderRadius = "0";
-  button.style.background = "transparent";
-  button.style.boxShadow = "none";
-  button.style.lineHeight = "0";
-  button.style.cursor = "pointer";
-  button.style.overflow = "visible";
-  button.style.flex = "0 0 auto";
-  button.style.opacity = active ? "0.92" : "0.6";
   button.style.color =
     viewerState.theme === "dark" ? "rgba(226, 232, 240, 0.74)" : "rgba(15, 23, 42, 0.52)";
-
-  const svg = button.querySelector<SVGElement>("svg");
-  if (!svg) {
-    return;
-  }
-  svg.style.display = "block";
-  svg.style.width = "16px";
-  svg.style.height = "16px";
-  svg.style.minWidth = "16px";
-  svg.style.minHeight = "16px";
-  svg.style.overflow = "visible";
-  svg.style.flex = "0 0 auto";
-  svg.style.color = "inherit";
-  svg.style.fill = "currentColor";
-  svg.style.pointerEvents = "none";
+  button.dataset.active = String(active);
 }
 
 function splitIcon(): string {
@@ -193,11 +163,6 @@ function themeIcon(theme: DiffTheme): string {
 function createToolbar(): HTMLElement {
   const toolbar = document.createElement("div");
   toolbar.className = "oc-diff-toolbar";
-  toolbar.style.display = "inline-flex";
-  toolbar.style.alignItems = "center";
-  toolbar.style.gap = "6px";
-  toolbar.style.marginInlineStart = "6px";
-  toolbar.style.flex = "0 0 auto";
 
   toolbar.append(
     createToolbarButton({