diff --git a/webui/src/components/thread/AgentActivityCluster.tsx b/webui/src/components/thread/AgentActivityCluster.tsx
index 3527437a4..bbba1045a 100644
--- a/webui/src/components/thread/AgentActivityCluster.tsx
+++ b/webui/src/components/thread/AgentActivityCluster.tsx
@@ -1776,7 +1776,10 @@ function FileEditRow({ edit }: { edit: FileEditSummary }) {
 
 function DiffPair({ added, deleted }: { added: number; deleted: number }) {
   return (
-    <span className="inline-flex shrink-0 translate-y-[0.055em] items-center gap-1.5 tabular-nums">
+    <span
+      className="inline-flex shrink-0 items-baseline gap-1.5 leading-[inherit] tabular-nums"
+      data-testid="activity-diff-pair"
+    >
       <DiffValue
         sign="+"
         value={added}
@@ -1794,8 +1797,11 @@ function DiffPair({ added, deleted }: { added: number; deleted: number }) {
 function DiffValue({ sign, value, className }: { sign: string; value: number; className: string }) {
   const safeValue = Number.isFinite(value) ? Math.max(0, Math.round(value)) : 0;
   return (
-    <span className={cn("inline-flex", className)} aria-label={`${sign}${safeValue}`}>
-      <span className="inline-flex" aria-hidden>
+    <span
+      className={cn("inline-flex items-baseline leading-[inherit]", className)}
+      aria-label={`${sign}${safeValue}`}
+    >
+      <span className="inline-flex items-baseline leading-none" aria-hidden>
         {sign}
         <AnimatedNumber value={safeValue} />
       </span>
@@ -1849,7 +1855,7 @@ function AnimatedNumber({ value }: { value: number }) {
 function RollingNumber({ value }: { value: number }) {
   const digits = String(value).split("");
   return (
-    <span className="inline-flex h-[1em] overflow-hidden align-[-0.13em]" aria-hidden>
+    <span className="inline-flex items-baseline leading-none" aria-hidden>
       {digits.map((digit, index) => (
         <RollingDigit
           key={`${digits.length}-${index}`}
@@ -1863,9 +1869,10 @@ function RollingNumber({ value }: { value: number }) {
 function RollingDigit({ digit }: { digit: number }) {
   const safeDigit = Number.isFinite(digit) ? Math.min(9, Math.max(0, digit)) : 0;
   return (
-    <span className="relative inline-block h-[1em] w-[0.62em] overflow-hidden">
+    <span className="relative inline-block h-[1em] w-[0.62em] overflow-hidden align-baseline leading-none">
+      <span className="invisible block h-[1em] leading-none">0</span>
       <span
-        className="flex flex-col transition-transform duration-200 ease-out will-change-transform"
+        className="absolute inset-x-0 top-0 flex flex-col transition-transform duration-200 ease-out will-change-transform"
         style={{ transform: `translateY(-${safeDigit}em)` }}
       >
         {Array.from({ length: 10 }, (_, n) => (
diff --git a/webui/src/tests/agent-activity-cluster.test.tsx b/webui/src/tests/agent-activity-cluster.test.tsx
index a07c8dd3b..4ae5bb899 100644
--- a/webui/src/tests/agent-activity-cluster.test.tsx
+++ b/webui/src/tests/agent-activity-cluster.test.tsx
@@ -334,6 +334,11 @@ describe("AgentActivityCluster", () => {
       const fileRef = screen.getByTestId("activity-file-reference");
       expect(fileRef).toHaveTextContent("src/app.tsx");
       expect(fileRef).toHaveAttribute("aria-label", "/Users/renxubin/project/src/app.tsx");
+      for (const diffPair of screen.getAllByTestId("activity-diff-pair")) {
+        expect(diffPair).toHaveClass("items-baseline");
+        expect(diffPair).toHaveClass("leading-[inherit]");
+        expect(diffPair.className).not.toContain("translate-y");
+      }
       await waitFor(() => {
         expect(screen.getAllByText("+12").length).toBeGreaterThan(0);
         expect(screen.getAllByText("-3").length).toBeGreaterThan(0);