diff --git a/archive/css/layout.css b/archive/css/layout.css
index 3ed4949..bc9ee69 100644
--- a/archive/css/layout.css
+++ b/archive/css/layout.css
@@ -5,18 +5,6 @@
     padding: 0.5rem 1rem;
 }
 
-.header-left {
-    display: flex;
-    align-items: center;
-    gap: 0.75rem;
-}
-
-.header-right {
-    display: flex;
-    gap: 0.5rem;
-    align-items: center;
-}
-
 .preview-toggle-label {
     display: flex;
     align-items: center;
diff --git a/classifier/css/layout.css b/classifier/css/layout.css
index c59dbb5..946ac78 100644
--- a/classifier/css/layout.css
+++ b/classifier/css/layout.css
@@ -81,13 +81,6 @@
     padding: 0.5rem 1rem;
 }
 
-.header-left,
-.header-right {
-    display: flex;
-    align-items: center;
-    gap: 0.5rem;
-}
-
 .header-divider {
     color: var(--border);
     margin: 0 0.25rem;
diff --git a/mdedit/css/base.css b/mdedit/css/base.css
index d1cdd9b..1fb1b75 100644
--- a/mdedit/css/base.css
+++ b/mdedit/css/base.css
@@ -221,14 +221,6 @@
     font-style: italic;
 }
 
-/* ── App header layout ────────────────────────────────────────────────────── */
-.header-left,
-.header-right {
-    display: flex;
-    align-items: center;
-    gap: 0.75rem;
-}
-
 /* ── Tailwind class overrides: use CSS tokens instead of hardcoded colours ── */
 /* bg-white / bg-gray-100 are used on the pane backgrounds in template.html.  */
 /* Override them here so they follow the design-token system (light + dark).   */
diff --git a/shared/base.css b/shared/base.css
index e2baba5..a09d7c8 100644
--- a/shared/base.css
+++ b/shared/base.css
@@ -275,6 +275,23 @@ a:hover {
     flex-shrink: 0;
 }
 
+/* Left and right groups inside .app-header. Both flex-row so their
+   children (logo, title, action button, theme icon, etc.) lay out
+   horizontally rather than stacking. Left side gets a slightly
+   larger gap because it carries the title group and an action
+   button; right side is just icon buttons. */
+.header-left {
+    display: flex;
+    align-items: center;
+    gap: 0.75rem;
+}
+
+.header-right {
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+}
+
 /* Tool name inside the header */
 .app-header__title {
     font-size: 17px;