diff --git a/workspaces/intelligent-assistant/.changeset/brave-dividers-show.md b/workspaces/intelligent-assistant/.changeset/brave-dividers-show.md
new file mode 100644
index 00000000000..6c4d4338b54
--- /dev/null
+++ b/workspaces/intelligent-assistant/.changeset/brave-dividers-show.md
@@ -0,0 +1,5 @@
+---
+'@red-hat-developer-hub/backstage-plugin-intelligent-assistant': patch
+---
+
+Restore missing visual separators in the notebook file attachments sidebar (RHDHBUGS-3511). Adds a horizontal divider between the notebook title and documents sections, a visible border on the drawer resize splitter, and a CSS fallback color when PatternFly theme variables are unavailable.
diff --git a/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/__tests__/DocumentSidebar.test.tsx b/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/__tests__/DocumentSidebar.test.tsx
index f01c397457f..d5e107cee95 100644
--- a/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/__tests__/DocumentSidebar.test.tsx
+++ b/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/__tests__/DocumentSidebar.test.tsx
@@ -55,6 +55,26 @@ describe('DocumentSidebar', () => {
     expect(screen.getByText('Test Notebook')).toBeInTheDocument();
   });
 
+  it('should render a separator between the title and documents sections', () => {
+    render(<DocumentSidebar {...defaultProps} />);
+    const separator = screen.getByRole('separator');
+    expect(separator).toBeInTheDocument();
+    expect(separator.className).toMatch(/sectionDivider/);
+    expect(
+      Array.from(document.styleSheets).some(sheet => {
+        try {
+          return Array.from(sheet.cssRules).some(rule =>
+            rule.cssText.includes(
+              '--pf-t--global--border--color--default, #c7c7c7',
+            ),
+          );
+        } catch {
+          return false;
+        }
+      }),
+    ).toBe(true);
+  });
+
   it('should render nothing when collapsed', () => {
     const { container } = render(
       <DocumentSidebar {...defaultProps} collapsed />,
diff --git a/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/notebooks/DocumentSidebar.tsx b/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/notebooks/DocumentSidebar.tsx
index 34111003bb8..7c92bb48fa0 100644
--- a/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/notebooks/DocumentSidebar.tsx
+++ b/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/notebooks/DocumentSidebar.tsx
@@ -47,9 +47,15 @@ const useStyles = makeStyles(theme => ({
     display: 'flex',
     alignItems: 'center',
     justifyContent: 'space-between',
-    marginBottom: theme.spacing(2),
     gap: theme.spacing(1),
   },
+  sectionDivider: {
+    borderTop: '1px solid var(--pf-t--global--border--color--default, #c7c7c7)',
+    marginTop: theme.spacing(2),
+    marginBottom: theme.spacing(2),
+    marginLeft: -theme.spacing(2),
+    marginRight: -theme.spacing(2),
+  },
   title: {
     fontWeight: 500,
     fontSize: '1.25rem',
@@ -178,6 +184,12 @@ export const DocumentSidebar = ({
         </Tooltip>
       </div>
 
+      <div
+        className={classes.sectionDivider}
+        role="separator"
+        aria-orientation="horizontal"
+      />
+
       <div className={classes.documentsRow}>
         <Typography className={classes.documentCount}>
           {t('notebook.view.documents.count', {
diff --git a/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/notebooks/NotebookView.tsx b/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/notebooks/NotebookView.tsx
index b07d0bd4688..7dc442bce77 100644
--- a/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/notebooks/NotebookView.tsx
+++ b/workspaces/intelligent-assistant/plugins/intelligent-assistant/src/components/notebooks/NotebookView.tsx
@@ -93,6 +93,7 @@ const useStyles = makeStyles(theme => ({
     '& .pf-v6-c-drawer__splitter, & .pf-v5-c-drawer__splitter': {
       backgroundColor:
         'var(--pf-t--global--background--color--floating--default)',
+      borderRight: '1px solid var(--pf-t--global--border--color--default)',
     },
   },
   expandStrip: {