diff --git a/packages/ui/src/components/message-stream-v2.tsx b/packages/ui/src/components/message-stream-v2.tsx
index 6f44df17..9a0dcf08 100644
--- a/packages/ui/src/components/message-stream-v2.tsx
+++ b/packages/ui/src/components/message-stream-v2.tsx
@@ -798,9 +798,7 @@ function StepCard(props: StepCardProps) {
     }
   }
 
-  type UsageInfo = NonNullable<ReturnType<typeof usageStats>>
-
-  const renderUsageChips = (usage: UsageInfo) => (
+  const renderUsageChips = (usage: NonNullable<ReturnType<typeof usageStats>>) => (
     <div class="message-step-usage">
       <div class="inline-flex items-center gap-1 rounded-full border border-[var(--border-base)] px-2 py-0.5 text-[10px]">
         <span class="uppercase text-[9px] tracking-wide text-[var(--text-muted)]">Input</span>
@@ -919,21 +917,27 @@ function ReasoningCard(props: ReasoningCardProps) {
   const toggle = () => setExpanded((prev) => !prev)
 
   return (
-    <div class="message-item-base assistant-message bg-[var(--message-assistant-bg)] border-l-4 border-[var(--message-assistant-border)]">
-      <div class="reasoning-card-header">
-        <div class="flex flex-col">
-          <span class="text-xs text-[var(--message-assistant-border)]">Thinking</span>
-        </div>
-        <div class="reasoning-card-header-right">
-          <button type="button" class="reasoning-card-toggle" onClick={toggle} aria-expanded={expanded()} aria-label={expanded() ? "Collapse thinking" : "Expand thinking"}>
-            {expanded() ? "Collapse" : "Expand"}
-          </button>
-          <span class="reasoning-card-time">{timestamp()}</span>
-        </div>
-      </div>
+    <div class="message-reasoning-card">
+      <button
+        type="button"
+        class="message-reasoning-toggle"
+        onClick={toggle}
+        aria-expanded={expanded()}
+        aria-label={expanded() ? "Collapse thinking" : "Expand thinking"}
+      >
+        <span class="message-reasoning-label">Thinking</span>
+        <span class="message-reasoning-meta">
+          <span class="message-reasoning-indicator">{expanded() ? "Hide" : "View"}</span>
+          <span class="message-reasoning-time">{timestamp()}</span>
+        </span>
+      </button>
+
       <Show when={expanded()}>
-        <div class="reasoning-card-body">
-          <pre class="reasoning-card-text">{reasoningText() || ""}</pre>
+        <div class="message-reasoning-expanded">
+          <div class="message-reasoning-divider" aria-hidden="true" />
+          <div class="message-reasoning-body">
+            <pre class="message-reasoning-text">{reasoningText() || ""}</pre>
+          </div>
         </div>
       </Show>
     </div>
diff --git a/packages/ui/src/styles/messaging/message-base.css b/packages/ui/src/styles/messaging/message-base.css
index 8450e2d6..ce7bb9c6 100644
--- a/packages/ui/src/styles/messaging/message-base.css
+++ b/packages/ui/src/styles/messaging/message-base.css
@@ -186,35 +186,108 @@
   @apply mt-4;
 }
 
-.reasoning-card-header {
-  @apply flex items-center justify-between;
+.message-reasoning-card {
+  background-color: var(--message-assistant-bg);
+  border-left: 4px solid var(--message-assistant-border);
+  margin-top: 0;
+  margin-bottom: 0;
+  padding: 0;
+  display: flex;
+  flex-direction: column;
+  gap: 0;
 }
 
-.reasoning-card-header-right {
-  @apply flex items-center gap-2;
-}
-
-.reasoning-card-toggle {
-  @apply inline-flex items-center justify-center rounded border border-[var(--border-base)] text-[var(--text-muted)] bg-transparent px-3 py-0.5 text-xs font-semibold;
-}
-
-.reasoning-card-toggle:hover {
-  color: var(--accent-primary);
-  border-color: var(--accent-primary);
-}
-
-.reasoning-card-time {
-  @apply text-[11px] text-[var(--text-muted)];
-}
-
-.reasoning-card-body {
-  @apply pt-1;
-}
-
-.reasoning-card-text {
-  @apply whitespace-pre-wrap break-words leading-[1.1] text-[var(--text-muted)] text-sm;
-  font-family: inherit;
-  background: transparent;
+.message-reasoning-toggle {
+  width: 100%;
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 0.65rem;
+  background: none;
   border: none;
+  padding: 0.25rem 0.6rem;
+  font: inherit;
+  color: inherit;
+  text-align: left;
+  cursor: pointer;
+  transition: background-color 0.2s ease, box-shadow 0.2s ease;
+}
+
+.message-reasoning-toggle:hover {
+  background-color: var(--surface-hover);
+}
+
+.message-reasoning-toggle:focus-visible {
+  outline: none;
+  box-shadow: 0 0 0 1px var(--accent-primary);
+}
+
+.message-reasoning-label {
+  font-size: 0.75rem;
+  font-weight: var(--font-weight-medium);
+  color: var(--message-assistant-border);
+}
+
+.message-reasoning-meta {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.5rem;
+}
+
+.message-reasoning-indicator {
+  line-height: 1;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 2.25rem;
+  height: 1.5rem;
+  padding: 0 0.65rem;
+  border: 1px solid var(--border-base);
+  border-radius: 0.375rem;
+  background-color: transparent;
+  color: var(--text-muted);
+  font-weight: var(--font-weight-semibold);
+  font-size: 0.85rem;
+  transition: color 0.2s ease, border-color 0.2s ease, background-color 0.2s ease, transform 0.2s ease;
+}
+
+.message-reasoning-toggle:hover .message-reasoning-indicator {
+  background-color: var(--surface-hover);
+  border-color: var(--accent-primary);
+  color: var(--accent-primary);
+}
+
+.message-reasoning-indicator:active {
+  transform: scale(0.97);
+}
+
+.message-reasoning-time {
+  font-size: 11px;
+  color: var(--text-muted);
+}
+
+.message-reasoning-expanded {
+  display: flex;
+  flex-direction: column;
+  gap: 0.35rem;
+}
+
+.message-reasoning-divider {
+  width: 100%;
+  height: 1px;
+  background-color: var(--border-base);
+}
+
+.message-reasoning-body {
+  padding: 0.25rem 0.6rem 0.4rem;
+}
+
+.message-reasoning-text {
+  font-family: var(--font-family-mono);
+  font-size: var(--font-size-sm);
+  line-height: var(--line-height-tight);
+  color: var(--text-muted);
+  white-space: pre-wrap;
+  margin: 0;
 }